summaryrefslogtreecommitdiff
path: root/plugins/AdvaImg/src/LibPNG/pngread.c
blob: 4b80ef2d46ce4b7d9dffc9454b8ccbc1c18c8972 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098

/* pngread.c - read a PNG file
 *
 * Last changed in libpng 1.6.10 [March 6, 2014]
 * Copyright (c) 1998-2014 Glenn Randers-Pehrson
 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
 *
 * This code is released under the libpng license.
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 *
 * This file contains routines that an application calls directly to
 * read a PNG file or stream.
 */

#include "pngpriv.h"
#if defined(PNG_SIMPLIFIED_READ_SUPPORTED) && defined(PNG_STDIO_SUPPORTED)
#  include <errno.h>
#endif

#ifdef PNG_READ_SUPPORTED

/* Create a PNG structure for reading, and allocate any memory needed. */
PNG_FUNCTION(png_structp,PNGAPI
png_create_read_struct,(png_const_charp user_png_ver, png_voidp error_ptr,
    png_error_ptr error_fn, png_error_ptr warn_fn),PNG_ALLOCATED)
{
#ifndef PNG_USER_MEM_SUPPORTED
   png_structp png_ptr = png_create_png_struct(user_png_ver, error_ptr,
      error_fn, warn_fn, NULL, NULL, NULL);
#else
   return png_create_read_struct_2(user_png_ver, error_ptr, error_fn,
       warn_fn, NULL, NULL, NULL);
}

/* Alternate create PNG structure for reading, and allocate any memory
 * needed.
 */
PNG_FUNCTION(png_structp,PNGAPI
png_create_read_struct_2,(png_const_charp user_png_ver, png_voidp error_ptr,
    png_error_ptr error_fn, png_error_ptr warn_fn, png_voidp mem_ptr,
    png_malloc_ptr malloc_fn, png_free_ptr free_fn),PNG_ALLOCATED)
{
   png_structp png_ptr = png_create_png_struct(user_png_ver, error_ptr,
      error_fn, warn_fn, mem_ptr, malloc_fn, free_fn);
#endif /* PNG_USER_MEM_SUPPORTED */

   if (png_ptr != NULL)
   {
      png_ptr->mode = PNG_IS_READ_STRUCT;

      /* Added in libpng-1.6.0; this can be used to detect a read structure if
       * required (it will be zero in a write structure.)
       */
#     ifdef PNG_SEQUENTIAL_READ_SUPPORTED
         png_ptr->IDAT_read_size = PNG_IDAT_READ_SIZE;
#     endif

#     ifdef PNG_BENIGN_READ_ERRORS_SUPPORTED
         png_ptr->flags |= PNG_FLAG_BENIGN_ERRORS_WARN;

         /* In stable builds only warn if an application error can be completely
          * handled.
          */
#        if PNG_LIBPNG_BUILD_BASE_TYPE >= PNG_LIBPNG_BUILD_RC
            png_ptr->flags |= PNG_FLAG_APP_WARNINGS_WARN;
#        endif
#     endif

      /* TODO: delay this, it can be done in png_init_io (if the app doesn't
       * do it itself) avoiding setting the default function if it is not
       * required.
       */
      png_set_read_fn(png_ptr, NULL, NULL);
   }

   return png_ptr;
}


#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
/* Read the information before the actual image data.  This has been
 * changed in v0.90 to allow reading a file that already has the magic
 * bytes read from the stream.  You can tell libpng how many bytes have
 * been read from the beginning of the stream (up to the maximum of 8)
 * via png_set_sig_bytes(), and we will only check the remaining bytes
 * here.  The application can then have access to the signature bytes we
 * read if it is determined that this isn't a valid PNG file.
 */
void PNGAPI
png_read_info(png_structrp png_ptr, png_inforp info_ptr)
{
#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
   int keep;
#endif

   png_debug(1, "in png_read_info");

   if (png_ptr == NULL || info_ptr == NULL)
      return;

   /* Read and check the PNG file signature. */
   png_read_sig(png_ptr, info_ptr);

   for (;;)
   {
      png_uint_32 length = png_read_chunk_header(png_ptr);
      png_uint_32 chunk_name = png_ptr->chunk_name;

      /* IDAT logic needs to happen here to simplify getting the two flags
       * right.
       */
      if (chunk_name == png_IDAT)
      {
         if (!(png_ptr->mode & PNG_HAVE_IHDR))
            png_chunk_error(png_ptr, "Missing IHDR before IDAT");

         else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
             !(png_ptr->mode & PNG_HAVE_PLTE))
            png_chunk_error(png_ptr, "Missing PLTE before IDAT");

         else if (png_ptr->mode & PNG_AFTER_IDAT)
            png_chunk_benign_error(png_ptr, "Too many IDATs found");

         png_ptr->mode |= PNG_HAVE_IDAT;
      }

      else if (png_ptr->mode & PNG_HAVE_IDAT)
         png_ptr->mode |= PNG_AFTER_IDAT;

      /* This should be a binary subdivision search or a hash for
       * matching the chunk name rather than a linear search.
       */
      if (chunk_name == png_IHDR)
         png_handle_IHDR(png_ptr, info_ptr, length);

      else if (chunk_name == png_IEND)
         png_handle_IEND(png_ptr, info_ptr, length);

#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
      else if ((keep = png_chunk_unknown_handling(png_ptr, chunk_name)) != 0)
      {
         png_handle_unknown(png_ptr, info_ptr, length, keep);

         if (chunk_name == png_PLTE)
            png_ptr->mode |= PNG_HAVE_PLTE;

         else if (chunk_name == png_IDAT)
         {
            png_ptr->idat_size = 0; /* It has been consumed */
            break;
         }
      }
#endif
      else if (chunk_name == png_PLTE)
         png_handle_PLTE(png_ptr, info_ptr, length);

      else if (chunk_name == png_IDAT)
      {
         png_ptr->idat_size = length;
         break;
      }

#ifdef PNG_READ_bKGD_SUPPORTED
      else if (chunk_name == png_bKGD)
         png_handle_bKGD(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_cHRM_SUPPORTED
      else if (chunk_name == png_cHRM)
         png_handle_cHRM(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_gAMA_SUPPORTED
      else if (chunk_name == png_gAMA)
         png_handle_gAMA(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_hIST_SUPPORTED
      else if (chunk_name == png_hIST)
         png_handle_hIST(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_oFFs_SUPPORTED
      else if (chunk_name == png_oFFs)
         png_handle_oFFs(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_pCAL_SUPPORTED
      else if (chunk_name == png_pCAL)
         png_handle_pCAL(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_sCAL_SUPPORTED
      else if (chunk_name == png_sCAL)
         png_handle_sCAL(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_pHYs_SUPPORTED
      else if (chunk_name == png_pHYs)
         png_handle_pHYs(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_sBIT_SUPPORTED
      else if (chunk_name == png_sBIT)
         png_handle_sBIT(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_sRGB_SUPPORTED
      else if (chunk_name == png_sRGB)
         png_handle_sRGB(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_iCCP_SUPPORTED
      else if (chunk_name == png_iCCP)
         png_handle_iCCP(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_sPLT_SUPPORTED
      else if (chunk_name == png_sPLT)
         png_handle_sPLT(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_tEXt_SUPPORTED
      else if (chunk_name == png_tEXt)
         png_handle_tEXt(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_tIME_SUPPORTED
      else if (chunk_name == png_tIME)
         png_handle_tIME(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_tRNS_SUPPORTED
      else if (chunk_name == png_tRNS)
         png_handle_tRNS(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_zTXt_SUPPORTED
      else if (chunk_name == png_zTXt)
         png_handle_zTXt(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_iTXt_SUPPORTED
      else if (chunk_name == png_iTXt)
         png_handle_iTXt(png_ptr, info_ptr, length);
#endif

      else
         png_handle_unknown(png_ptr, info_ptr, length,
            PNG_HANDLE_CHUNK_AS_DEFAULT);
   }
}
#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

/* Optional call to update the users info_ptr structure */
void PNGAPI
png_read_update_info(png_structrp png_ptr, png_inforp info_ptr)
{
   png_debug(1, "in png_read_update_info");

   if (png_ptr != NULL)
   {
      if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0)
      {
         png_read_start_row(png_ptr);

#        ifdef PNG_READ_TRANSFORMS_SUPPORTED
            png_read_transform_info(png_ptr, info_ptr);
#        else
            PNG_UNUSED(info_ptr)
#        endif
      }

      /* New in 1.6.0 this avoids the bug of doing the initializations twice */
      else
         png_app_error(png_ptr,
            "png_read_update_info/png_start_read_image: duplicate call");
   }
}

#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
/* Initialize palette, background, etc, after transformations
 * are set, but before any reading takes place.  This allows
 * the user to obtain a gamma-corrected palette, for example.
 * If the user doesn't call this, we will do it ourselves.
 */
void PNGAPI
png_start_read_image(png_structrp png_ptr)
{
   png_debug(1, "in png_start_read_image");

   if (png_ptr != NULL)
   {
      if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0)
         png_read_start_row(png_ptr);

      /* New in 1.6.0 this avoids the bug of doing the initializations twice */
      else
         png_app_error(png_ptr,
            "png_start_read_image/png_read_update_info: duplicate call");
   }
}
#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
#ifdef PNG_MNG_FEATURES_SUPPORTED
/* Undoes intrapixel differencing,
 * NOTE: this is apparently only supported in the 'sequential' reader.
 */
static void
png_do_read_intrapixel(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_read_intrapixel");

   if (
       (row_info->color_type & PNG_COLOR_MASK_COLOR))
   {
      int bytes_per_pixel;
      png_uint_32 row_width = row_info->width;

      if (row_info->bit_depth == 8)
      {
         png_bytep rp;
         png_uint_32 i;

         if (row_info->color_type == PNG_COLOR_TYPE_RGB)
            bytes_per_pixel = 3;

         else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
            bytes_per_pixel = 4;

         else
            return;

         for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
         {
            *(rp) = (png_byte)((256 + *rp + *(rp + 1)) & 0xff);
            *(rp+2) = (png_byte)((256 + *(rp + 2) + *(rp + 1)) & 0xff);
         }
      }
      else if (row_info->bit_depth == 16)
      {
         png_bytep rp;
         png_uint_32 i;

         if (row_info->color_type == PNG_COLOR_TYPE_RGB)
            bytes_per_pixel = 6;

         else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
            bytes_per_pixel = 8;

         else
            return;

         for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
         {
            png_uint_32 s0   = (*(rp    ) << 8) | *(rp + 1);
            png_uint_32 s1   = (*(rp + 2) << 8) | *(rp + 3);
            png_uint_32 s2   = (*(rp + 4) << 8) | *(rp + 5);
            png_uint_32 red  = (s0 + s1 + 65536) & 0xffff;
            png_uint_32 blue = (s2 + s1 + 65536) & 0xffff;
            *(rp    ) = (png_byte)((red >> 8) & 0xff);
            *(rp + 1) = (png_byte)(red & 0xff);
            *(rp + 4) = (png_byte)((blue >> 8) & 0xff);
            *(rp + 5) = (png_byte)(blue & 0xff);
         }
      }
   }
}
#endif /* PNG_MNG_FEATURES_SUPPORTED */

void PNGAPI
png_read_row(png_structrp png_ptr, png_bytep row, png_bytep dsp_row)
{
   png_row_info row_info;

   if (png_ptr == NULL)
      return;

   png_debug2(1, "in png_read_row (row %lu, pass %d)",
       (unsigned long)png_ptr->row_number, png_ptr->pass);

   /* png_read_start_row sets the information (in particular iwidth) for this
    * interlace pass.
    */
   if (!(png_ptr->flags & PNG_FLAG_ROW_INIT))
      png_read_start_row(png_ptr);

   /* 1.5.6: row_info moved out of png_struct to a local here. */
   row_info.width = png_ptr->iwidth; /* NOTE: width of current interlaced row */
   row_info.color_type = png_ptr->color_type;
   row_info.bit_depth = png_ptr->bit_depth;
   row_info.channels = png_ptr->channels;
   row_info.pixel_depth = png_ptr->pixel_depth;
   row_info.rowbytes = PNG_ROWBYTES(row_info.pixel_depth, row_info.width);

   if (png_ptr->row_number == 0 && png_ptr->pass == 0)
   {
   /* Check for transforms that have been set but were defined out */
#if defined(PNG_WRITE_INVERT_SUPPORTED) && !defined(PNG_READ_INVERT_SUPPORTED)
   if (png_ptr->transformations & PNG_INVERT_MONO)
      png_warning(png_ptr, "PNG_READ_INVERT_SUPPORTED is not defined");
#endif

#if defined(PNG_WRITE_FILLER_SUPPORTED) && !defined(PNG_READ_FILLER_SUPPORTED)
   if (png_ptr->transformations & PNG_FILLER)
      png_warning(png_ptr, "PNG_READ_FILLER_SUPPORTED is not defined");
#endif

#if defined(PNG_WRITE_PACKSWAP_SUPPORTED) && \
    !defined(PNG_READ_PACKSWAP_SUPPORTED)
   if (png_ptr->transformations & PNG_PACKSWAP)
      png_warning(png_ptr, "PNG_READ_PACKSWAP_SUPPORTED is not defined");
#endif

#if defined(PNG_WRITE_PACK_SUPPORTED) && !defined(PNG_READ_PACK_SUPPORTED)
   if (png_ptr->transformations & PNG_PACK)
      png_warning(png_ptr, "PNG_READ_PACK_SUPPORTED is not defined");
#endif

#if defined(PNG_WRITE_SHIFT_SUPPORTED) && !defined(PNG_READ_SHIFT_SUPPORTED)
   if (png_ptr->transformations & PNG_SHIFT)
      png_warning(png_ptr, "PNG_READ_SHIFT_SUPPORTED is not defined");
#endif

#if defined(PNG_WRITE_BGR_SUPPORTED) && !defined(PNG_READ_BGR_SUPPORTED)
   if (png_ptr->transformations & PNG_BGR)
      png_warning(png_ptr, "PNG_READ_BGR_SUPPORTED is not defined");
#endif

#if defined(PNG_WRITE_SWAP_SUPPORTED) && !defined(PNG_READ_SWAP_SUPPORTED)
   if (png_ptr->transformations & PNG_SWAP_BYTES)
      png_warning(png_ptr, "PNG_READ_SWAP_SUPPORTED is not defined");
#endif
   }

#ifdef PNG_READ_INTERLACING_SUPPORTED
   /* If interlaced and we do not need a new row, combine row and return.
    * Notice that the pixels we have from previous rows have been transformed
    * already; we can only combine like with like (transformed or
    * untransformed) and, because of the libpng API for interlaced images, this
    * means we must transform before de-interlacing.
    */
   if (png_ptr->interlaced && (png_ptr->transformations & PNG_INTERLACE))
   {
      switch (png_ptr->pass)
      {
         case 0:
            if (png_ptr->row_number & 0x07)
            {
               if (dsp_row != NULL)
                  png_combine_row(png_ptr, dsp_row, 1/*display*/);
               png_read_finish_row(png_ptr);
               return;
            }
            break;

         case 1:
            if ((png_ptr->row_number & 0x07) || png_ptr->width < 5)
            {
               if (dsp_row != NULL)
                  png_combine_row(png_ptr, dsp_row, 1/*display*/);

               png_read_finish_row(png_ptr);
               return;
            }
            break;

         case 2:
            if ((png_ptr->row_number & 0x07) != 4)
            {
               if (dsp_row != NULL && (png_ptr->row_number & 4))
                  png_combine_row(png_ptr, dsp_row, 1/*display*/);

               png_read_finish_row(png_ptr);
               return;
            }
            break;

         case 3:
            if ((png_ptr->row_number & 3) || png_ptr->width < 3)
            {
               if (dsp_row != NULL)
                  png_combine_row(png_ptr, dsp_row, 1/*display*/);

               png_read_finish_row(png_ptr);
               return;
            }
            break;

         case 4:
            if ((png_ptr->row_number & 3) != 2)
            {
               if (dsp_row != NULL && (png_ptr->row_number & 2))
                  png_combine_row(png_ptr, dsp_row, 1/*display*/);

               png_read_finish_row(png_ptr);
               return;
            }
            break;

         case 5:
            if ((png_ptr->row_number & 1) || png_ptr->width < 2)
            {
               if (dsp_row != NULL)
                  png_combine_row(png_ptr, dsp_row, 1/*display*/);

               png_read_finish_row(png_ptr);
               return;
            }
            break;

         default:
         case 6:
            if (!(png_ptr->row_number & 1))
            {
               png_read_finish_row(png_ptr);
               return;
            }
            break;
      }
   }
#endif

   if (!(png_ptr->mode & PNG_HAVE_IDAT))
      png_error(png_ptr, "Invalid attempt to read row data");

   /* Fill the row with IDAT data: */
   png_read_IDAT_data(png_ptr, png_ptr->row_buf, row_info.rowbytes + 1);

   if (png_ptr->row_buf[0] > PNG_FILTER_VALUE_NONE)
   {
      if (png_ptr->row_buf[0] < PNG_FILTER_VALUE_LAST)
         png_read_filter_row(png_ptr, &row_info, png_ptr->row_buf + 1,
            png_ptr->prev_row + 1, png_ptr->row_buf[0]);
      else
         png_error(png_ptr, "bad adaptive filter value");
   }

   /* libpng 1.5.6: the following line was copying png_ptr->rowbytes before
    * 1.5.6, while the buffer really is this big in current versions of libpng
    * it may not be in the future, so this was changed just to copy the
    * interlaced count:
    */
   memcpy(png_ptr->prev_row, png_ptr->row_buf, row_info.rowbytes + 1);

#ifdef PNG_MNG_FEATURES_SUPPORTED
   if ((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&
       (png_ptr->filter_type == PNG_INTRAPIXEL_DIFFERENCING))
   {
      /* Intrapixel differencing */
      png_do_read_intrapixel(&row_info, png_ptr->row_buf + 1);
   }
#endif

#ifdef PNG_READ_TRANSFORMS_SUPPORTED
   if (png_ptr->transformations)
      png_do_read_transformations(png_ptr, &row_info);
#endif

   /* The transformed pixel depth should match the depth now in row_info. */
   if (png_ptr->transformed_pixel_depth == 0)
   {
      png_ptr->transformed_pixel_depth = row_info.pixel_depth;
      if (row_info.pixel_depth > png_ptr->maximum_pixel_depth)
         png_error(png_ptr, "sequential row overflow");
   }

   else if (png_ptr->transformed_pixel_depth != row_info.pixel_depth)
      png_error(png_ptr, "internal sequential row size calculation error");

#ifdef PNG_READ_INTERLACING_SUPPORTED
   /* Blow up interlaced rows to full size */
   if (png_ptr->interlaced &&
      (png_ptr->transformations & PNG_INTERLACE))
   {
      if (png_ptr->pass < 6)
         png_do_read_interlace(&row_info, png_ptr->row_buf + 1, png_ptr->pass,
            png_ptr->transformations);

      if (dsp_row != NULL)
         png_combine_row(png_ptr, dsp_row, 1/*display*/);

      if (row != NULL)
         png_combine_row(png_ptr, row, 0/*row*/);
   }

   else
#endif
   {
      if (row != NULL)
         png_combine_row(png_ptr, row, -1/*ignored*/);

      if (dsp_row != NULL)
         png_combine_row(png_ptr, dsp_row, -1/*ignored*/);
   }
   png_read_finish_row(png_ptr);

   if (png_ptr->read_row_fn != NULL)
      (*(png_ptr->read_row_fn))(png_ptr, png_ptr->row_number, png_ptr->pass);

}
#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
/* Read one or more rows of image data.  If the image is interlaced,
 * and png_set_interlace_handling() has been called, the rows need to
 * contain the contents of the rows from the previous pass.  If the
 * image has alpha or transparency, and png_handle_alpha()[*] has been
 * called, the rows contents must be initialized to the contents of the
 * screen.
 *
 * "row" holds the actual image, and pixels are placed in it
 * as they arrive.  If the image is displayed after each pass, it will
 * appear to "sparkle" in.  "display_row" can be used to display a
 * "chunky" progressive image, with finer detail added as it becomes
 * available.  If you do not want this "chunky" display, you may pass
 * NULL for display_row.  If you do not want the sparkle display, and
 * you have not called png_handle_alpha(), you may pass NULL for rows.
 * If you have called png_handle_alpha(), and the image has either an
 * alpha channel or a transparency chunk, you must provide a buffer for
 * rows.  In this case, you do not have to provide a display_row buffer
 * also, but you may.  If the image is not interlaced, or if you have
 * not called png_set_interlace_handling(), the display_row buffer will
 * be ignored, so pass NULL to it.
 *
 * [*] png_handle_alpha() does not exist yet, as of this version of libpng
 */

void PNGAPI
png_read_rows(png_structrp png_ptr, png_bytepp row,
    png_bytepp display_row, png_uint_32 num_rows)
{
   png_uint_32 i;
   png_bytepp rp;
   png_bytepp dp;

   png_debug(1, "in png_read_rows");

   if (png_ptr == NULL)
      return;

   rp = row;
   dp = display_row;
   if (rp != NULL && dp != NULL)
      for (i = 0; i < num_rows; i++)
      {
         png_bytep rptr = *rp++;
         png_bytep dptr = *dp++;

         png_read_row(png_ptr, rptr, dptr);
      }

   else if (rp != NULL)
      for (i = 0; i < num_rows; i++)
      {
         png_bytep rptr = *rp;
         png_read_row(png_ptr, rptr, NULL);
         rp++;
      }

   else if (dp != NULL)
      for (i = 0; i < num_rows; i++)
      {
         png_bytep dptr = *dp;
         png_read_row(png_ptr, NULL, dptr);
         dp++;
      }
}
#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
/* Read the entire image.  If the image has an alpha channel or a tRNS
 * chunk, and you have called png_handle_alpha()[*], you will need to
 * initialize the image to the current image that PNG will be overlaying.
 * We set the num_rows again here, in case it was incorrectly set in
 * png_read_start_row() by a call to png_read_update_info() or
 * png_start_read_image() if png_set_interlace_handling() wasn't called
 * prior to either of these functions like it should have been.  You can
 * only call this function once.  If you desire to have an image for
 * each pass of a interlaced image, use png_read_rows() instead.
 *
 * [*] png_handle_alpha() does not exist yet, as of this version of libpng
 */
void PNGAPI
png_read_image(png_structrp png_ptr, png_bytepp image)
{
   png_uint_32 i, image_height;
   int pass, j;
   png_bytepp rp;

   png_debug(1, "in png_read_image");

   if (png_ptr == NULL)
      return;

#ifdef PNG_READ_INTERLACING_SUPPORTED
   if (!(png_ptr->flags & PNG_FLAG_ROW_INIT))
   {
      pass = png_set_interlace_handling(png_ptr);
      /* And make sure transforms are initialized. */
      png_start_read_image(png_ptr);
   }
   else
   {
      if (png_ptr->interlaced && !(png_ptr->transformations & PNG_INTERLACE))
      {
         /* Caller called png_start_read_image or png_read_update_info without
          * first turning on the PNG_INTERLACE transform.  We can fix this here,
          * but the caller should do it!
          */
         png_warning(png_ptr, "Interlace handling should be turned on when "
            "using png_read_image");
         /* Make sure this is set correctly */
         png_ptr->num_rows = png_ptr->height;
      }

      /* Obtain the pass number, which also turns on the PNG_INTERLACE flag in
       * the above error case.
       */
      pass = png_set_interlace_handling(png_ptr);
   }
#else
   if (png_ptr->interlaced)
      png_error(png_ptr,
          "Cannot read interlaced image -- interlace handler disabled");

   pass = 1;
#endif

   image_height=png_ptr->height;

   for (j = 0; j < pass; j++)
   {
      rp = image;
      for (i = 0; i < image_height; i++)
      {
         png_read_row(png_ptr, *rp, NULL);
         rp++;
      }
   }
}
#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
/* Read the end of the PNG file.  Will not read past the end of the
 * file, will verify the end is accurate, and will read any comments
 * or time information at the end of the file, if info is not NULL.
 */
void PNGAPI
png_read_end(png_structrp png_ptr, png_inforp info_ptr)
{
#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
   int keep;
#endif

   png_debug(1, "in png_read_end");

   if (png_ptr == NULL)
      return;

   /* If png_read_end is called in the middle of reading the rows there may
    * still be pending IDAT data and an owned zstream.  Deal with this here.
    */
#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
   if (!png_chunk_unknown_handling(png_ptr, png_IDAT))
#endif
      png_read_finish_IDAT(png_ptr);

#ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
   /* Report invalid palette index; added at libng-1.5.10 */
   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
      png_ptr->num_palette_max > png_ptr->num_palette)
     png_benign_error(png_ptr, "Read palette index exceeding num_palette");
#endif

   do
   {
      png_uint_32 length = png_read_chunk_header(png_ptr);
      png_uint_32 chunk_name = png_ptr->chunk_name;

      if (chunk_name == png_IEND)
         png_handle_IEND(png_ptr, info_ptr, length);

      else if (chunk_name == png_IHDR)
         png_handle_IHDR(png_ptr, info_ptr, length);

      else if (info_ptr == NULL)
         png_crc_finish(png_ptr, length);

#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
      else if ((keep = png_chunk_unknown_handling(png_ptr, chunk_name)) != 0)
      {
         if (chunk_name == png_IDAT)
         {
            if ((length > 0) || (png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT))
               png_benign_error(png_ptr, "Too many IDATs found");
         }
         png_handle_unknown(png_ptr, info_ptr, length, keep);
         if (chunk_name == png_PLTE)
            png_ptr->mode |= PNG_HAVE_PLTE;
      }
#endif

      else if (chunk_name == png_IDAT)
      {
         /* Zero length IDATs are legal after the last IDAT has been
          * read, but not after other chunks have been read.
          */
         if ((length > 0) || (png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT))
            png_benign_error(png_ptr, "Too many IDATs found");

         png_crc_finish(png_ptr, length);
      }
      else if (chunk_name == png_PLTE)
         png_handle_PLTE(png_ptr, info_ptr, length);

#ifdef PNG_READ_bKGD_SUPPORTED
      else if (chunk_name == png_bKGD)
         png_handle_bKGD(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_cHRM_SUPPORTED
      else if (chunk_name == png_cHRM)
         png_handle_cHRM(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_gAMA_SUPPORTED
      else if (chunk_name == png_gAMA)
         png_handle_gAMA(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_hIST_SUPPORTED
      else if (chunk_name == png_hIST)
         png_handle_hIST(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_oFFs_SUPPORTED
      else if (chunk_name == png_oFFs)
         png_handle_oFFs(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_pCAL_SUPPORTED
      else if (chunk_name == png_pCAL)
         png_handle_pCAL(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_sCAL_SUPPORTED
      else if (chunk_name == png_sCAL)
         png_handle_sCAL(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_pHYs_SUPPORTED
      else if (chunk_name == png_pHYs)
         png_handle_pHYs(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_sBIT_SUPPORTED
      else if (chunk_name == png_sBIT)
         png_handle_sBIT(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_sRGB_SUPPORTED
      else if (chunk_name == png_sRGB)
         png_handle_sRGB(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_iCCP_SUPPORTED
      else if (chunk_name == png_iCCP)
         png_handle_iCCP(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_sPLT_SUPPORTED
      else if (chunk_name == png_sPLT)
         png_handle_sPLT(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_tEXt_SUPPORTED
      else if (chunk_name == png_tEXt)
         png_handle_tEXt(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_tIME_SUPPORTED
      else if (chunk_name == png_tIME)
         png_handle_tIME(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_tRNS_SUPPORTED
      else if (chunk_name == png_tRNS)
         png_handle_tRNS(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_zTXt_SUPPORTED
      else if (chunk_name == png_zTXt)
         png_handle_zTXt(png_ptr, info_ptr, length);
#endif

#ifdef PNG_READ_iTXt_SUPPORTED
      else if (chunk_name == png_iTXt)
         png_handle_iTXt(png_ptr, info_ptr, length);
#endif

      else
         png_handle_unknown(png_ptr, info_ptr, length,
            PNG_HANDLE_CHUNK_AS_DEFAULT);
   } while (!(png_ptr->mode & PNG_HAVE_IEND));
}
#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

/* Free all memory used in the read struct */
static void
png_read_destroy(png_structrp png_ptr)
{
   png_debug(1, "in png_read_destroy");

#ifdef PNG_READ_GAMMA_SUPPORTED
   png_destroy_gamma_table(png_ptr);
#endif

   png_free(png_ptr, png_ptr->big_row_buf);
   png_free(png_ptr, png_ptr->big_prev_row);
   png_free(png_ptr, png_ptr->read_buffer);

#ifdef PNG_READ_QUANTIZE_SUPPORTED
   png_free(png_ptr, png_ptr->palette_lookup);
   png_free(png_ptr, png_ptr->quantize_index);
#endif

   if (png_ptr->free_me & PNG_FREE_PLTE)
      png_zfree(png_ptr, png_ptr->palette);
   png_ptr->free_me &= ~PNG_FREE_PLTE;

#if defined(PNG_tRNS_SUPPORTED) || \
    defined(PNG_READ_EXPAND_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
   if (png_ptr->free_me & PNG_FREE_TRNS)
      png_free(png_ptr, png_ptr->trans_alpha);
   png_ptr->free_me &= ~PNG_FREE_TRNS;
#endif

   inflateEnd(&png_ptr->zstream);

#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
   png_free(png_ptr, png_ptr->save_buffer);
#endif

#if defined(PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED) &&\
   defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)
   png_free(png_ptr, png_ptr->unknown_chunk.data);
#endif

#ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
   png_free(png_ptr, png_ptr->chunk_list);
#endif

   /* NOTE: the 'setjmp' buffer may still be allocated and the memory and error
    * callbacks are still set at this point.  They are required to complete the
    * destruction of the png_struct itself.
    */
}

/* Free all memory used by the read */
void PNGAPI
png_destroy_read_struct(png_structpp png_ptr_ptr, png_infopp info_ptr_ptr,
    png_infopp end_info_ptr_ptr)
{
   png_structrp png_ptr = NULL;

   png_debug(1, "in png_destroy_read_struct");

   if (png_ptr_ptr != NULL)
      png_ptr = *png_ptr_ptr;

   if (png_ptr == NULL)
      return;

   /* libpng 1.6.0: use the API to destroy info structs to ensure consistent
    * behavior.  Prior to 1.6.0 libpng did extra 'info' destruction in this API.
    * The extra was, apparently, unnecessary yet this hides memory leak bugs.
    */
   png_destroy_info_struct(png_ptr, end_info_ptr_ptr);
   png_destroy_info_struct(png_ptr, info_ptr_ptr);

   *png_ptr_ptr = NULL;
   png_read_destroy(png_ptr);
   png_destroy_png_struct(png_ptr);
}

void PNGAPI
png_set_read_status_fn(png_structrp png_ptr, png_read_status_ptr read_row_fn)
{
   if (png_ptr == NULL)
      return;

   png_ptr->read_row_fn = read_row_fn;
}


#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
#ifdef PNG_INFO_IMAGE_SUPPORTED
void PNGAPI
png_read_png(png_structrp png_ptr, png_inforp info_ptr,
                           int transforms,
                           voidp params)
{
   if (png_ptr == NULL || info_ptr == NULL)
      return;

   /* png_read_info() gives us all of the information from the
    * PNG file before the first IDAT (image data chunk).
    */
   png_read_info(png_ptr, info_ptr);
   if (info_ptr->height > PNG_UINT_32_MAX/(sizeof (png_bytep)))
      png_error(png_ptr, "Image is too high to process with png_read_png()");

   /* -------------- image transformations start here ------------------- */
   /* libpng 1.6.10: add code to cause a png_app_error if a selected TRANSFORM
    * is not implemented.  This will only happen in de-configured (non-default)
    * libpng builds.  The results can be unexpected - png_read_png may return
    * short or mal-formed rows because the transform is skipped.
    */

   /* Tell libpng to strip 16-bit/color files down to 8 bits per color.
    */
   if (transforms & PNG_TRANSFORM_SCALE_16)
     /* Added at libpng-1.5.4. "strip_16" produces the same result that it
      * did in earlier versions, while "scale_16" is now more accurate.
      */
#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
      png_set_scale_16(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_SCALE_16 not supported");
#endif

   /* If both SCALE and STRIP are required pngrtran will effectively cancel the
    * latter by doing SCALE first.  This is ok and allows apps not to check for
    * which is supported to get the right answer.
    */
   if (transforms & PNG_TRANSFORM_STRIP_16)
#ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
      png_set_strip_16(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_STRIP_16 not supported");
#endif

   /* Strip alpha bytes from the input data without combining with
    * the background (not recommended).
    */
   if (transforms & PNG_TRANSFORM_STRIP_ALPHA)
#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
      png_set_strip_alpha(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_STRIP_ALPHA not supported");
#endif

   /* Extract multiple pixels with bit depths of 1, 2, or 4 from a single
    * byte into separate bytes (useful for paletted and grayscale images).
    */
   if (transforms & PNG_TRANSFORM_PACKING)
#ifdef PNG_READ_PACK_SUPPORTED
      png_set_packing(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_PACKING not supported");
#endif

   /* Change the order of packed pixels to least significant bit first
    * (not useful if you are using png_set_packing).
    */
   if (transforms & PNG_TRANSFORM_PACKSWAP)
#ifdef PNG_READ_PACKSWAP_SUPPORTED
      png_set_packswap(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_PACKSWAP not supported");
#endif

   /* Expand paletted colors into true RGB triplets
    * Expand grayscale images to full 8 bits from 1, 2, or 4 bits/pixel
    * Expand paletted or RGB images with transparency to full alpha
    * channels so the data will be available as RGBA quartets.
    */
   if (transforms & PNG_TRANSFORM_EXPAND)
#ifdef PNG_READ_EXPAND_SUPPORTED
      png_set_expand(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_EXPAND not supported");
#endif

   /* We don't handle background color or gamma transformation or quantizing.
    */

   /* Invert monochrome files to have 0 as white and 1 as black
    */
   if (transforms & PNG_TRANSFORM_INVERT_MONO)
#ifdef PNG_READ_INVERT_SUPPORTED
      png_set_invert_mono(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_INVERT_MONO not supported");
#endif

   /* If you want to shift the pixel values from the range [0,255] or
    * [0,65535] to the original [0,7] or [0,31], or whatever range the
    * colors were originally in:
    */
   if (transforms & PNG_TRANSFORM_SHIFT)
#ifdef PNG_READ_SHIFT_SUPPORTED
      if (info_ptr->valid & PNG_INFO_sBIT)
         png_set_shift(png_ptr, &info_ptr->sig_bit);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_SHIFT not supported");
#endif

   /* Flip the RGB pixels to BGR (or RGBA to BGRA) */
   if (transforms & PNG_TRANSFORM_BGR)
#ifdef PNG_READ_BGR_SUPPORTED
      png_set_bgr(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_BGR not supported");
#endif

   /* Swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */
   if (transforms & PNG_TRANSFORM_SWAP_ALPHA)
#ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
      png_set_swap_alpha(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_SWAP_ALPHA not supported");
#endif

   /* Swap bytes of 16-bit files to least significant byte first */
   if (transforms & PNG_TRANSFORM_SWAP_ENDIAN)
#ifdef PNG_READ_SWAP_SUPPORTED
      png_set_swap(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_SWAP_ENDIAN not supported");
#endif

/* Added at libpng-1.2.41 */
   /* Invert the alpha channel from opacity to transparency */
   if (transforms & PNG_TRANSFORM_INVERT_ALPHA)
#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
      png_set_invert_alpha(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_INVERT_ALPHA not supported");
#endif

/* Added at libpng-1.2.41 */
   /* Expand grayscale image to RGB */
   if (transforms & PNG_TRANSFORM_GRAY_TO_RGB)
#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
      png_set_gray_to_rgb(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_GRAY_TO_RGB not supported");
#endif

/* Added at libpng-1.5.4 */
   if (transforms & PNG_TRANSFORM_EXPAND_16)
#ifdef PNG_READ_EXPAND_16_SUPPORTED
      png_set_expand_16(png_ptr);
#else
      png_app_error(png_ptr, "PNG_TRANSFORM_EXPAND_16 not supported");
#endif

   /* We don't handle adding filler bytes */

   /* We use png_read_image and rely on that for interlace handling, but we also
    * call png_read_update_info therefore must turn on interlace handling now:
    */
   (void)png_set_interlace_handling(png_ptr);

   /* Optional call to gamma correct and add the background to the palette
    * and update info structure.  REQUIRED if you are expecting libpng to
    * update the palette for you (i.e., you selected such a transform above).
    */
   png_read_update_info(png_ptr, info_ptr);

   /* -------------- image transformations end here ------------------- */

   png_free_data(png_ptr, info_ptr, PNG_FREE_ROWS, 0);
   if (info_ptr->row_pointers == NULL)
   {
      png_uint_32 iptr;

      info_ptr->row_pointers = png_voidcast(png_bytepp, png_malloc(png_ptr,
          info_ptr->height * (sizeof (png_bytep))));

      for (iptr=0; iptr<info_ptr->height; iptr++)
         info_ptr->row_pointers[iptr] = NULL;

      info_ptr->free_me |= PNG_FREE_ROWS;

      for (iptr = 0; iptr < info_ptr->height; iptr++)
         info_ptr->row_pointers[iptr] = png_voidcast(png_bytep,
            png_malloc(png_ptr, info_ptr->rowbytes));
   }

   png_read_image(png_ptr, info_ptr->row_pointers);
   info_ptr->valid |= PNG_INFO_IDAT;

   /* Read rest of file, and get additional chunks in info_ptr - REQUIRED */
   png_read_end(png_ptr, info_ptr);

   PNG_UNUSED(params)
}
#endif /* PNG_INFO_IMAGE_SUPPORTED */
#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

#ifdef PNG_SIMPLIFIED_READ_SUPPORTED
/* SIMPLIFIED READ
 *
 * This code currently relies on the sequential reader, though it could easily
 * be made to work with the progressive one.
 */
/* Arguments to png_image_finish_read: */

/* Encoding of PNG data (used by the color-map code) */
#  define P_NOTSET  0 /* File encoding not yet known */
#  define P_sRGB    1 /* 8-bit encoded to sRGB gamma */
#  define P_LINEAR  2 /* 16-bit linear: not encoded, NOT pre-multiplied! */
#  define P_FILE    3 /* 8-bit encoded to file gamma, not sRGB or linear */
#  define P_LINEAR8 4 /* 8-bit linear: only from a file value */

/* Color-map processing: after libpng has run on the PNG image further
 * processing may be needed to conver the data to color-map indicies.
 */
#define PNG_CMAP_NONE      0
#define PNG_CMAP_GA        1 /* Process GA data to a color-map with alpha */
#define PNG_CMAP_TRANS     2 /* Process GA data to a background index */
#define PNG_CMAP_RGB       3 /* Process RGB data */
#define PNG_CMAP_RGB_ALPHA 4 /* Process RGBA data */

/* The following document where the background is for each processing case. */
#define PNG_CMAP_NONE_BACKGROUND      256
#define PNG_CMAP_GA_BACKGROUND        231
#define PNG_CMAP_TRANS_BACKGROUND     254
#define PNG_CMAP_RGB_BACKGROUND       256
#define PNG_CMAP_RGB_ALPHA_BACKGROUND 216

typedef struct
{
   /* Arguments: */
   png_imagep image;
   png_voidp  buffer;
   png_int_32 row_stride;
   png_voidp  colormap;
   png_const_colorp background;
   /* Local variables: */
   png_voidp       local_row;
   png_voidp       first_row;
   ptrdiff_t       row_bytes;           /* step between rows */
   int             file_encoding;       /* E_ values above */
   png_fixed_point gamma_to_linear;     /* For P_FILE, reciprocal of gamma */
   int             colormap_processing; /* PNG_CMAP_ values above */
} png_image_read_control;

/* Do all the *safe* initialization - 'safe' means that png_error won't be
 * called, so setting up the jmp_buf is not required.  This means that anything
 * called from here must *not* call png_malloc - it has to call png_malloc_warn
 * instead so that control is returned safely back to this routine.
 */
static int
png_image_read_init(png_imagep image)
{
   if (image->opaque == NULL)
   {
      png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, image,
          png_safe_error, png_safe_warning);

      /* And set the rest of the structure to NULL to ensure that the various
       * fields are consistent.
       */
      memset(image, 0, (sizeof *image));
      image->version = PNG_IMAGE_VERSION;

      if (png_ptr != NULL)
      {
         png_infop info_ptr = png_create_info_struct(png_ptr);

         if (info_ptr != NULL)
         {
            png_controlp control = png_voidcast(png_controlp,
               png_malloc_warn(png_ptr, (sizeof *control)));

            if (control != NULL)
            {
               memset(control, 0, (sizeof *control));

               control->png_ptr = png_ptr;
               control->info_ptr = info_ptr;
               control->for_write = 0;

               image->opaque = control;
               return 1;
            }

            /* Error clean up */
            png_destroy_info_struct(png_ptr, &info_ptr);
         }

         png_destroy_read_struct(&png_ptr, NULL, NULL);
      }

      return png_image_error(image, "png_image_read: out of memory");
   }

   return png_image_error(image, "png_image_read: opaque pointer not NULL");
}

/* Utility to find the base format of a PNG file from a png_struct. */
static png_uint_32
png_image_format(png_structrp png_ptr)
{
   png_uint_32 format = 0;

   if (png_ptr->color_type & PNG_COLOR_MASK_COLOR)
      format |= PNG_FORMAT_FLAG_COLOR;

   if (png_ptr->color_type & PNG_COLOR_MASK_ALPHA)
      format |= PNG_FORMAT_FLAG_ALPHA;

   /* Use png_ptr here, not info_ptr, because by examination png_handle_tRNS
    * sets the png_struct fields; that's all we are interested in here.  The
    * precise interaction with an app call to png_set_tRNS and PNG file reading
    * is unclear.
    */
   else if (png_ptr->num_trans > 0)
      format |= PNG_FORMAT_FLAG_ALPHA;

   if (png_ptr->bit_depth == 16)
      format |= PNG_FORMAT_FLAG_LINEAR;

   if (png_ptr->color_type & PNG_COLOR_MASK_PALETTE)
      format |= PNG_FORMAT_FLAG_COLORMAP;

   return format;
}

/* Is the given gamma significantly different from sRGB?  The test is the same
 * one used in pngrtran.c when deciding whether to do gamma correction.  The
 * arithmetic optimizes the division by using the fact that the inverse of the
 * file sRGB gamma is 2.2
 */
static int
png_gamma_not_sRGB(png_fixed_point g)
{
   if (g < PNG_FP_1)
   {
      /* An uninitialized gamma is assumed to be sRGB for the simplified API. */
      if (g == 0)
         return 0;

      return png_gamma_significant((g * 11 + 2)/5 /* i.e. *2.2, rounded */);
   }

   return 1;
}

/* Do the main body of a 'png_image_begin_read' function; read the PNG file
 * header and fill in all the information.  This is executed in a safe context,
 * unlike the init routine above.
 */
static int
png_image_read_header(png_voidp argument)
{
   png_imagep image = png_voidcast(png_imagep, argument);
   png_structrp png_ptr = image->opaque->png_ptr;
   png_inforp info_ptr = image->opaque->info_ptr;

   png_set_benign_errors(png_ptr, 1/*warn*/);
   png_read_info(png_ptr, info_ptr);

   /* Do this the fast way; just read directly out of png_struct. */
   image->width = png_ptr->width;
   image->height = png_ptr->height;

   {
      png_uint_32 format = png_image_format(png_ptr);

      image->format = format;

#ifdef PNG_COLORSPACE_SUPPORTED
      /* Does the colorspace match sRGB?  If there is no color endpoint
       * (colorant) information assume yes, otherwise require the
       * 'ENDPOINTS_MATCHP_sRGB' colorspace flag to have been set.  If the
       * colorspace has been determined to be invalid ignore it.
       */
      if ((format & PNG_FORMAT_FLAG_COLOR) != 0 && ((png_ptr->colorspace.flags
         & (PNG_COLORSPACE_HAVE_ENDPOINTS|PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB|
            PNG_COLORSPACE_INVALID)) == PNG_COLORSPACE_HAVE_ENDPOINTS))
         image->flags |= PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB;
#endif
   }

   /* We need the maximum number of entries regardless of the format the
    * application sets here.
    */
   {
      png_uint_32 cmap_entries;

      switch (png_ptr->color_type)
      {
         case PNG_COLOR_TYPE_GRAY:
            cmap_entries = 1U << png_ptr->bit_depth;
            break;

         case PNG_COLOR_TYPE_PALETTE:
            cmap_entries = png_ptr->num_palette;
            break;

         default:
            cmap_entries = 256;
            break;
      }

      if (cmap_entries > 256)
         cmap_entries = 256;

      image->colormap_entries = cmap_entries;
   }

   return 1;
}

#ifdef PNG_STDIO_SUPPORTED
int PNGAPI
png_image_begin_read_from_stdio(png_imagep image, FILE* file)
{
   if (image != NULL && image->version == PNG_IMAGE_VERSION)
   {
      if (file != NULL)
      {
         if (png_image_read_init(image))
         {
            /* This is slightly evil, but png_init_io doesn't do anything other
             * than this and we haven't changed the standard IO functions so
             * this saves a 'safe' function.
             */
            image->opaque->png_ptr->io_ptr = file;
            return png_safe_execute(image, png_image_read_header, image);
         }
      }

      else
         return png_image_error(image,
            "png_image_begin_read_from_stdio: invalid argument");
   }

   else if (image != NULL)
      return png_image_error(image,
         "png_image_begin_read_from_stdio: incorrect PNG_IMAGE_VERSION");

   return 0;
}

int PNGAPI
png_image_begin_read_from_file(png_imagep image, const char *file_name)
{
   if (image != NULL && image->version == PNG_IMAGE_VERSION)
   {
      if (file_name != NULL)
      {
         FILE *fp = fopen(file_name, "rb");

         if (fp != NULL)
         {
            if (png_image_read_init(image))
            {
               image->opaque->png_ptr->io_ptr = fp;
               image->opaque->owned_file = 1;
               return png_safe_execute(image, png_image_read_header, image);
            }

            /* Clean up: just the opened file. */
            (void)fclose(fp);
         }

         else
            return png_image_error(image, strerror(errno));
      }

      else
         return png_image_error(image,
            "png_image_begin_read_from_file: invalid argument");
   }

   else if (image != NULL)
      return png_image_error(image,
         "png_image_begin_read_from_file: incorrect PNG_IMAGE_VERSION");

   return 0;
}
#endif /* PNG_STDIO_SUPPORTED */

static void PNGCBAPI
png_image_memory_read(png_structp png_ptr, png_bytep out, png_size_t need)
{
   if (png_ptr != NULL)
   {
      png_imagep image = png_voidcast(png_imagep, png_ptr->io_ptr);
      if (image != NULL)
      {
         png_controlp cp = image->opaque;
         if (cp != NULL)
         {
            png_const_bytep memory = cp->memory;
            png_size_t size = cp->size;

            if (memory != NULL && size >= need)
            {
               memcpy(out, memory, need);
               cp->memory = memory + need;
               cp->size = size - need;
               return;
            }

            png_error(png_ptr, "read beyond end of data");
         }
      }

      png_error(png_ptr, "invalid memory read");
   }
}

int PNGAPI png_image_begin_read_from_memory(png_imagep image,
   png_const_voidp memory, png_size_t size)
{
   if (image != NULL && image->version == PNG_IMAGE_VERSION)
   {
      if (memory != NULL && size > 0)
      {
         if (png_image_read_init(image))
         {
            /* Now set the IO functions to read from the memory buffer and
             * store it into io_ptr.  Again do this in-place to avoid calling a
             * libpng function that requires error handling.
             */
            image->opaque->memory = png_voidcast(png_const_bytep, memory);
            image->opaque->size = size;
            image->opaque->png_ptr->io_ptr = image;
            image->opaque->png_ptr->read_data_fn = png_image_memory_read;

            return png_safe_execute(image, png_image_read_header, image);
         }
      }

      else
         return png_image_error(image,
            "png_image_begin_read_from_memory: invalid argument");
   }

   else if (image != NULL)
      return png_image_error(image,
         "png_image_begin_read_from_memory: incorrect PNG_IMAGE_VERSION");

   return 0;
}

/* Utility function to skip chunks that are not used by the simplified image
 * read functions and an appropriate macro to call it.
 */
#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
static void
png_image_skip_unused_chunks(png_structrp png_ptr)
{
   /* Prepare the reader to ignore all recognized chunks whose data will not
    * be used, i.e., all chunks recognized by libpng except for those
    * involved in basic image reading:
    *
    *    IHDR, PLTE, IDAT, IEND
    *
    * Or image data handling:
    *
    *    tRNS, bKGD, gAMA, cHRM, sRGB, [iCCP] and sBIT.
    *
    * This provides a small performance improvement and eliminates any
    * potential vulnerability to security problems in the unused chunks.
    *
    * At present the iCCP chunk data isn't used, so iCCP chunk can be ignored
    * too.  This allows the simplified API to be compiled without iCCP support,
    * however if the support is there the chunk is still checked to detect
    * errors (which are unfortunately quite common.)
    */
   {
         static PNG_CONST png_byte chunks_to_process[] = {
            98,  75,  71,  68, '\0',  /* bKGD */
            99,  72,  82,  77, '\0',  /* cHRM */
           103,  65,  77,  65, '\0',  /* gAMA */
#        ifdef PNG_READ_iCCP_SUPPORTED
           105,  67,  67,  80, '\0',  /* iCCP */
#        endif
           115,  66,  73,  84, '\0',  /* sBIT */
           115,  82,  71,  66, '\0',  /* sRGB */
           };

       /* Ignore unknown chunks and all other chunks except for the
        * IHDR, PLTE, tRNS, IDAT, and IEND chunks.
        */
       png_set_keep_unknown_chunks(png_ptr, PNG_HANDLE_CHUNK_NEVER,
         NULL, -1);

       /* But do not ignore image data handling chunks */
       png_set_keep_unknown_chunks(png_ptr, PNG_HANDLE_CHUNK_AS_DEFAULT,
         chunks_to_process, (sizeof chunks_to_process)/5);
    }
}

#  define PNG_SKIP_CHUNKS(p) png_image_skip_unused_chunks(p)
#else
#  define PNG_SKIP_CHUNKS(p) ((void)0)
#endif /* PNG_HANDLE_AS_UNKNOWN_SUPPORTED */

/* The following macro gives the exact rounded answer for all values in the
 * range 0..255 (it actually divides by 51.2, but the rounding still generates
 * the correct numbers 0..5
 */
#define PNG_DIV51(v8) (((v8) * 5 + 130) >> 8)

/* Utility functions to make particular color-maps */
static void
set_file_encoding(png_image_read_control *display)
{
   png_fixed_point g = display->image->opaque->png_ptr->colorspace.gamma;
   if (png_gamma_significant(g))
   {
      if (png_gamma_not_sRGB(g))
      {
         display->file_encoding = P_FILE;
         display->gamma_to_linear = png_reciprocal(g);
      }

      else
         display->file_encoding = P_sRGB;
   }

   else
      display->file_encoding = P_LINEAR8;
}

static unsigned int
decode_gamma(png_image_read_control *display, png_uint_32 value, int encoding)
{
   if (encoding == P_FILE) /* double check */
      encoding = display->file_encoding;

   if (encoding == P_NOTSET) /* must be the file encoding */
   {
      set_file_encoding(display);
      encoding = display->file_encoding;
   }

   switch (encoding)
   {
      case P_FILE:
         value = png_gamma_16bit_correct(value*257, display->gamma_to_linear);
         break;

      case P_sRGB:
         value = png_sRGB_table[value];
         break;

      case P_LINEAR:
         break;

      case P_LINEAR8:
         value *= 257;
         break;

      default:
         png_error(display->image->opaque->png_ptr,
            "unexpected encoding (internal error)");
         break;
   }

   return value;
}

static png_uint_32
png_colormap_compose(png_image_read_control *display,
   png_uint_32 foreground, int foreground_encoding, png_uint_32 alpha,
   png_uint_32 background, int encoding)
{
   /* The file value is composed on the background, the background has the given
    * encoding and so does the result, the file is encoded with P_FILE and the
    * file and alpha are 8-bit values.  The (output) encoding will always be
    * P_LINEAR or P_sRGB.
    */
   png_uint_32 f = decode_gamma(display, foreground, foreground_encoding);
   png_uint_32 b = decode_gamma(display, background, encoding);

   /* The alpha is always an 8-bit value (it comes from the palette), the value
    * scaled by 255 is what PNG_sRGB_FROM_LINEAR requires.
    */
   f = f * alpha + b * (255-alpha);

   if (encoding == P_LINEAR)
   {
      /* Scale to 65535; divide by 255, approximately (in fact this is extremely
       * accurate, it divides by 255.00000005937181414556, with no overflow.)
       */
      f *= 257; /* Now scaled by 65535 */
      f += f >> 16;
      f = (f+32768) >> 16;
   }

   else /* P_sRGB */
      f = PNG_sRGB_FROM_LINEAR(f);

   return f;
}

/* NOTE: P_LINEAR values to this routine must be 16-bit, but P_FILE values must
 * be 8-bit.
 */
static void
png_create_colormap_entry(png_image_read_control *display,
   png_uint_32 ip, png_uint_32 red, png_uint_32 green, png_uint_32 blue,
   png_uint_32 alpha, int encoding)
{
   png_imagep image = display->image;
   const int output_encoding = (image->format & PNG_FORMAT_FLAG_LINEAR) ?
      P_LINEAR : P_sRGB;
   const int convert_to_Y = (image->format & PNG_FORMAT_FLAG_COLOR) == 0 &&
      (red != green || green != blue);

   if (ip > 255)
      png_error(image->opaque->png_ptr, "color-map index out of range");

   /* Update the cache with whether the file gamma is significantly different
    * from sRGB.
    */
   if (encoding == P_FILE)
   {
      if (display->file_encoding == P_NOTSET)
         set_file_encoding(display);

      /* Note that the cached value may be P_FILE too, but if it is then the
       * gamma_to_linear member has been set.
       */
      encoding = display->file_encoding;
   }

   if (encoding == P_FILE)
   {
      png_fixed_point g = display->gamma_to_linear;

      red = png_gamma_16bit_correct(red*257, g);
      green = png_gamma_16bit_correct(green*257, g);
      blue = png_gamma_16bit_correct(blue*257, g);

      if (convert_to_Y || output_encoding == P_LINEAR)
      {
         alpha *= 257;
         encoding = P_LINEAR;
      }

      else
      {
         red = PNG_sRGB_FROM_LINEAR(red * 255);
         green = PNG_sRGB_FROM_LINEAR(green * 255);
         blue = PNG_sRGB_FROM_LINEAR(blue * 255);
         encoding = P_sRGB;
      }
   }

   else if (encoding == P_LINEAR8)
   {
      /* This encoding occurs quite frequently in test cases because PngSuite
       * includes a gAMA 1.0 chunk with most images.
       */
      red *= 257;
      green *= 257;
      blue *= 257;
      alpha *= 257;
      encoding = P_LINEAR;
   }

   else if (encoding == P_sRGB && (convert_to_Y || output_encoding == P_LINEAR))
   {
      /* The values are 8-bit sRGB values, but must be converted to 16-bit
       * linear.
       */
      red = png_sRGB_table[red];
      green = png_sRGB_table[green];
      blue = png_sRGB_table[blue];
      alpha *= 257;
      encoding = P_LINEAR;
   }

   /* This is set if the color isn't gray but the output is. */
   if (encoding == P_LINEAR)
   {
      if (convert_to_Y)
      {
         /* NOTE: these values are copied from png_do_rgb_to_gray */
         png_uint_32 y = (png_uint_32)6968 * red  + (png_uint_32)23434 * green +
            (png_uint_32)2366 * blue;

         if (output_encoding == P_LINEAR)
            y = (y + 16384) >> 15;

         else
         {
            /* y is scaled by 32768, we need it scaled by 255: */
            y = (y + 128) >> 8;
            y *= 255;
            y = PNG_sRGB_FROM_LINEAR((y + 64) >> 7);
            encoding = P_sRGB;
         }

         blue = red = green = y;
      }

      else if (output_encoding == P_sRGB)
      {
         red = PNG_sRGB_FROM_LINEAR(red * 255);
         green = PNG_sRGB_FROM_LINEAR(green * 255);
         blue = PNG_sRGB_FROM_LINEAR(blue * 255);
         alpha = PNG_DIV257(alpha);
         encoding = P_sRGB;
      }
   }

   if (encoding != output_encoding)
      png_error(image->opaque->png_ptr, "bad encoding (internal error)");

   /* Store the value. */
   {
#     ifdef PNG_FORMAT_AFIRST_SUPPORTED
         const int afirst = (image->format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
            (image->format & PNG_FORMAT_FLAG_ALPHA) != 0;
#     else
#        define afirst 0
#     endif
#     ifdef PNG_FORMAT_BGR_SUPPORTED
         const int bgr = (image->format & PNG_FORMAT_FLAG_BGR) ? 2 : 0;
#     else
#        define bgr 0
#     endif

      if (output_encoding == P_LINEAR)
      {
         png_uint_16p entry = png_voidcast(png_uint_16p, display->colormap);

         entry += ip * PNG_IMAGE_SAMPLE_CHANNELS(image->format);

         /* The linear 16-bit values must be pre-multiplied by the alpha channel
          * value, if less than 65535 (this is, effectively, composite on black
          * if the alpha channel is removed.)
          */
         switch (PNG_IMAGE_SAMPLE_CHANNELS(image->format))
         {
            case 4:
               entry[afirst ? 0 : 3] = (png_uint_16)alpha;
               /* FALL THROUGH */

            case 3:
               if (alpha < 65535)
               {
                  if (alpha > 0)
                  {
                     blue = (blue * alpha + 32767U)/65535U;
                     green = (green * alpha + 32767U)/65535U;
                     red = (red * alpha + 32767U)/65535U;
                  }

                  else
                     red = green = blue = 0;
               }
               entry[afirst + (2 ^ bgr)] = (png_uint_16)blue;
               entry[afirst + 1] = (png_uint_16)green;
               entry[afirst + bgr] = (png_uint_16)red;
               break;

            case 2:
               entry[1 ^ afirst] = (png_uint_16)alpha;
               /* FALL THROUGH */

            case 1:
               if (alpha < 65535)
               {
                  if (alpha > 0)
                     green = (green * alpha + 32767U)/65535U;

                  else
                     green = 0;
               }
               entry[afirst] = (png_uint_16)green;
               break;

            default:
               break;
         }
      }

      else /* output encoding is P_sRGB */
      {
         png_bytep entry = png_voidcast(png_bytep, display->colormap);

         entry += ip * PNG_IMAGE_SAMPLE_CHANNELS(image->format);

         switch (PNG_IMAGE_SAMPLE_CHANNELS(image->format))
         {
            case 4:
               entry[afirst ? 0 : 3] = (png_byte)alpha;
            case 3:
               entry[afirst + (2 ^ bgr)] = (png_byte)blue;
               entry[afirst + 1] = (png_byte)green;
               entry[afirst + bgr] = (png_byte)red;
               break;

            case 2:
               entry[1 ^ afirst] = (png_byte)alpha;
            case 1:
               entry[afirst] = (png_byte)green;
               break;

            default:
               break;
         }
      }

#     ifdef afirst
#        undef afirst
#     endif
#     ifdef bgr
#        undef bgr
#     endif
   }
}

static int
make_gray_file_colormap(png_image_read_control *display)
{
   unsigned int i;

   for (i=0; i<256; ++i)
      png_create_colormap_entry(display, i, i, i, i, 255, P_FILE);

   return i;
}

static int
make_gray_colormap(png_image_read_control *display)
{
   unsigned int i;

   for (i=0; i<256; ++i)
      png_create_colormap_entry(display, i, i, i, i, 255, P_sRGB);

   return i;
}
#define PNG_GRAY_COLORMAP_ENTRIES 256

static int
make_ga_colormap(png_image_read_control *display)
{
   unsigned int i, a;

   /* Alpha is retained, the output will be a color-map with entries
    * selected by six levels of alpha.  One transparent entry, 6 gray
    * levels for all the intermediate alpha values, leaving 230 entries
    * for the opaque grays.  The color-map entries are the six values
    * [0..5]*51, the GA processing uses PNG_DIV51(value) to find the
    * relevant entry.
    *
    * if (alpha > 229) // opaque
    * {
    *    // The 231 entries are selected to make the math below work:
    *    base = 0;
    *    entry = (231 * gray + 128) >> 8;
    * }
    * else if (alpha < 26) // transparent
    * {
    *    base = 231;
    *    entry = 0;
    * }
    * else // partially opaque
    * {
    *    base = 226 + 6 * PNG_DIV51(alpha);
    *    entry = PNG_DIV51(gray);
    * }
    */
   i = 0;
   while (i < 231)
   {
      unsigned int gray = (i * 256 + 115) / 231;
      png_create_colormap_entry(display, i++, gray, gray, gray, 255, P_sRGB);
   }

   /* 255 is used here for the component values for consistency with the code
    * that undoes premultiplication in pngwrite.c.
    */
   png_create_colormap_entry(display, i++, 255, 255, 255, 0, P_sRGB);

   for (a=1; a<5; ++a)
   {
      unsigned int g;

      for (g=0; g<6; ++g)
         png_create_colormap_entry(display, i++, g*51, g*51, g*51, a*51,
            P_sRGB);
   }

   return i;
}

#define PNG_GA_COLORMAP_ENTRIES 256

static int
make_rgb_colormap(png_image_read_control *display)
{
   unsigned int i, r;

   /* Build a 6x6x6 opaque RGB cube */
   for (i=r=0; r<6; ++r)
   {
      unsigned int g;

      for (g=0; g<6; ++g)
      {
         unsigned int b;

         for (b=0; b<6; ++b)
            png_create_colormap_entry(display, i++, r*51, g*51, b*51, 255,
               P_sRGB);
      }
   }

   return i;
}

#define PNG_RGB_COLORMAP_ENTRIES 216

/* Return a palette index to the above palette given three 8-bit sRGB values. */
#define PNG_RGB_INDEX(r,g,b) \
   ((png_byte)(6 * (6 * PNG_DIV51(r) + PNG_DIV51(g)) + PNG_DIV51(b)))

static int
png_image_read_colormap(png_voidp argument)
{
   png_image_read_control *display =
      png_voidcast(png_image_read_control*, argument);
   const png_imagep image = display->image;

   const png_structrp png_ptr = image->opaque->png_ptr;
   const png_uint_32 output_format = image->format;
   const int output_encoding = (output_format & PNG_FORMAT_FLAG_LINEAR) ?
      P_LINEAR : P_sRGB;

   unsigned int cmap_entries;
   unsigned int output_processing;        /* Output processing option */
   unsigned int data_encoding = P_NOTSET; /* Encoding libpng must produce */

   /* Background information; the background color and the index of this color
    * in the color-map if it exists (else 256).
    */
   unsigned int background_index = 256;
   png_uint_32 back_r, back_g, back_b;

   /* Flags to accumulate things that need to be done to the input. */
   int expand_tRNS = 0;

   /* Exclude the NYI feature of compositing onto a color-mapped buffer; it is
    * very difficult to do, the results look awful, and it is difficult to see
    * what possible use it is because the application can't control the
    * color-map.
    */
   if (((png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0 ||
         png_ptr->num_trans > 0) /* alpha in input */ &&
      ((output_format & PNG_FORMAT_FLAG_ALPHA) == 0) /* no alpha in output */)
   {
      if (output_encoding == P_LINEAR) /* compose on black */
         back_b = back_g = back_r = 0;

      else if (display->background == NULL /* no way to remove it */)
         png_error(png_ptr,
            "a background color must be supplied to remove alpha/transparency");

      /* Get a copy of the background color (this avoids repeating the checks
       * below.)  The encoding is 8-bit sRGB or 16-bit linear, depending on the
       * output format.
       */
      else
      {
         back_g = display->background->green;
         if (output_format & PNG_FORMAT_FLAG_COLOR)
         {
            back_r = display->background->red;
            back_b = display->background->blue;
         }
         else
            back_b = back_r = back_g;
      }
   }

   else if (output_encoding == P_LINEAR)
      back_b = back_r = back_g = 65535;

   else
      back_b = back_r = back_g = 255;

   /* Default the input file gamma if required - this is necessary because
    * libpng assumes that if no gamma information is present the data is in the
    * output format, but the simplified API deduces the gamma from the input
    * format.
    */
   if ((png_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_GAMMA) == 0)
   {
      /* Do this directly, not using the png_colorspace functions, to ensure
       * that it happens even if the colorspace is invalid (though probably if
       * it is the setting will be ignored)  Note that the same thing can be
       * achieved at the application interface with png_set_gAMA.
       */
      if (png_ptr->bit_depth == 16 &&
         (image->flags & PNG_IMAGE_FLAG_16BIT_sRGB) == 0)
         png_ptr->colorspace.gamma = PNG_GAMMA_LINEAR;

      else
         png_ptr->colorspace.gamma = PNG_GAMMA_sRGB_INVERSE;

      png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
   }

   /* Decide what to do based on the PNG color type of the input data.  The
    * utility function png_create_colormap_entry deals with most aspects of the
    * output transformations; this code works out how to produce bytes of
    * color-map entries from the original format.
    */
   switch (png_ptr->color_type)
   {
      case PNG_COLOR_TYPE_GRAY:
         if (png_ptr->bit_depth <= 8)
         {
            /* There at most 256 colors in the output, regardless of
             * transparency.
             */
            unsigned int step, i, val, trans = 256/*ignore*/, back_alpha = 0;

            cmap_entries = 1U << png_ptr->bit_depth;
            if (cmap_entries > image->colormap_entries)
               png_error(png_ptr, "gray[8] color-map: too few entries");

            step = 255 / (cmap_entries - 1);
            output_processing = PNG_CMAP_NONE;

            /* If there is a tRNS chunk then this either selects a transparent
             * value or, if the output has no alpha, the background color.
             */
            if (png_ptr->num_trans > 0)
            {
               trans = png_ptr->trans_color.gray;

               if ((output_format & PNG_FORMAT_FLAG_ALPHA) == 0)
                  back_alpha = output_encoding == P_LINEAR ? 65535 : 255;
            }

            /* png_create_colormap_entry just takes an RGBA and writes the
             * corresponding color-map entry using the format from 'image',
             * including the required conversion to sRGB or linear as
             * appropriate.  The input values are always either sRGB (if the
             * gamma correction flag is 0) or 0..255 scaled file encoded values
             * (if the function must gamma correct them).
             */
            for (i=val=0; i<cmap_entries; ++i, val += step)
            {
               /* 'i' is a file value.  While this will result in duplicated
                * entries for 8-bit non-sRGB encoded files it is necessary to
                * have non-gamma corrected values to do tRNS handling.
                */
               if (i != trans)
                  png_create_colormap_entry(display, i, val, val, val, 255,
                     P_FILE/*8-bit with file gamma*/);

               /* Else this entry is transparent.  The colors don't matter if
                * there is an alpha channel (back_alpha == 0), but it does no
                * harm to pass them in; the values are not set above so this
                * passes in white.
                *
                * NOTE: this preserves the full precision of the application
                * supplied background color when it is used.
                */
               else
                  png_create_colormap_entry(display, i, back_r, back_g, back_b,
                     back_alpha, output_encoding);
            }

            /* We need libpng to preserve the original encoding. */
            data_encoding = P_FILE;

            /* The rows from libpng, while technically gray values, are now also
             * color-map indicies; however, they may need to be expanded to 1
             * byte per pixel.  This is what png_set_packing does (i.e., it
             * unpacks the bit values into bytes.)
             */
            if (png_ptr->bit_depth < 8)
               png_set_packing(png_ptr);
         }

         else /* bit depth is 16 */
         {
            /* The 16-bit input values can be converted directly to 8-bit gamma
             * encoded values; however, if a tRNS chunk is present 257 color-map
             * entries are required.  This means that the extra entry requires
             * special processing; add an alpha channel, sacrifice gray level
             * 254 and convert transparent (alpha==0) entries to that.
             *
             * Use libpng to chop the data to 8 bits.  Convert it to sRGB at the
             * same time to minimize quality loss.  If a tRNS chunk is present
             * this means libpng must handle it too; otherwise it is impossible
             * to do the exact match on the 16-bit value.
             *
             * If the output has no alpha channel *and* the background color is
             * gray then it is possible to let libpng handle the substitution by
             * ensuring that the corresponding gray level matches the background
             * color exactly.
             */
            data_encoding = P_sRGB;

            if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
               png_error(png_ptr, "gray[16] color-map: too few entries");

            cmap_entries = make_gray_colormap(display);

            if (png_ptr->num_trans > 0)
            {
               unsigned int back_alpha;

               if (output_format & PNG_FORMAT_FLAG_ALPHA)
                  back_alpha = 0;

               else
               {
                  if (back_r == back_g && back_g == back_b)
                  {
                     /* Background is gray; no special processing will be
                      * required.
                      */
                     png_color_16 c;
                     png_uint_32 gray = back_g;

                     if (output_encoding == P_LINEAR)
                     {
                        gray = PNG_sRGB_FROM_LINEAR(gray * 255);

                        /* And make sure the corresponding palette entry
                         * matches.
                         */
                        png_create_colormap_entry(display, gray, back_g, back_g,
                           back_g, 65535, P_LINEAR);
                     }

                     /* The background passed to libpng, however, must be the
                      * sRGB value.
                      */
                     c.index = 0; /*unused*/
                     c.gray = c.red = c.green = c.blue = (png_uint_16)gray;

                     /* NOTE: does this work without expanding tRNS to alpha?
                      * It should be the color->gray case below apparently
                      * doesn't.
                      */
                     png_set_background_fixed(png_ptr, &c,
                        PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                        0/*gamma: not used*/);

                     output_processing = PNG_CMAP_NONE;
                     break;
                  }

                  back_alpha = output_encoding == P_LINEAR ? 65535 : 255;
               }

               /* output_processing means that the libpng-processed row will be
                * 8-bit GA and it has to be processing to single byte color-map
                * values.  Entry 254 is replaced by either a completely
                * transparent entry or by the background color at full
                * precision (and the background color is not a simple gray leve
                * in this case.)
                */
               expand_tRNS = 1;
               output_processing = PNG_CMAP_TRANS;
               background_index = 254;

               /* And set (overwrite) color-map entry 254 to the actual
                * background color at full precision.
                */
               png_create_colormap_entry(display, 254, back_r, back_g, back_b,
                  back_alpha, output_encoding);
            }

            else
               output_processing = PNG_CMAP_NONE;
         }
         break;

      case PNG_COLOR_TYPE_GRAY_ALPHA:
         /* 8-bit or 16-bit PNG with two channels - gray and alpha.  A minimum
          * of 65536 combinations.  If, however, the alpha channel is to be
          * removed there are only 256 possibilities if the background is gray.
          * (Otherwise there is a subset of the 65536 possibilities defined by
          * the triangle between black, white and the background color.)
          *
          * Reduce 16-bit files to 8-bit and sRGB encode the result.  No need to
          * worry about tRNS matching - tRNS is ignored if there is an alpha
          * channel.
          */
         data_encoding = P_sRGB;

         if (output_format & PNG_FORMAT_FLAG_ALPHA)
         {
            if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
               png_error(png_ptr, "gray+alpha color-map: too few entries");

            cmap_entries = make_ga_colormap(display);

            background_index = PNG_CMAP_GA_BACKGROUND;
            output_processing = PNG_CMAP_GA;
         }

         else /* alpha is removed */
         {
            /* Alpha must be removed as the PNG data is processed when the
             * background is a color because the G and A channels are
             * independent and the vector addition (non-parallel vectors) is a
             * 2-D problem.
             *
             * This can be reduced to the same algorithm as above by making a
             * colormap containing gray levels (for the opaque grays), a
             * background entry (for a transparent pixel) and a set of four six
             * level color values, one set for each intermediate alpha value.
             * See the comments in make_ga_colormap for how this works in the
             * per-pixel processing.
             *
             * If the background is gray, however, we only need a 256 entry gray
             * level color map.  It is sufficient to make the entry generated
             * for the background color be exactly the color specified.
             */
            if ((output_format & PNG_FORMAT_FLAG_COLOR) == 0 ||
               (back_r == back_g && back_g == back_b))
            {
               /* Background is gray; no special processing will be required. */
               png_color_16 c;
               png_uint_32 gray = back_g;

               if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
                  png_error(png_ptr, "gray-alpha color-map: too few entries");

               cmap_entries = make_gray_colormap(display);

               if (output_encoding == P_LINEAR)
               {
                  gray = PNG_sRGB_FROM_LINEAR(gray * 255);

                  /* And make sure the corresponding palette entry matches. */
                  png_create_colormap_entry(display, gray, back_g, back_g,
                     back_g, 65535, P_LINEAR);
               }

               /* The background passed to libpng, however, must be the sRGB
                * value.
                */
               c.index = 0; /*unused*/
               c.gray = c.red = c.green = c.blue = (png_uint_16)gray;

               png_set_background_fixed(png_ptr, &c,
                  PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                  0/*gamma: not used*/);

               output_processing = PNG_CMAP_NONE;
            }

            else
            {
               png_uint_32 i, a;

               /* This is the same as png_make_ga_colormap, above, except that
                * the entries are all opaque.
                */
               if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
                  png_error(png_ptr, "ga-alpha color-map: too few entries");

               i = 0;
               while (i < 231)
               {
                  png_uint_32 gray = (i * 256 + 115) / 231;
                  png_create_colormap_entry(display, i++, gray, gray, gray,
                     255, P_sRGB);
               }

               /* NOTE: this preserves the full precision of the application
                * background color.
                */
               background_index = i;
               png_create_colormap_entry(display, i++, back_r, back_g, back_b,
                  output_encoding == P_LINEAR ? 65535U : 255U, output_encoding);

               /* For non-opaque input composite on the sRGB background - this
                * requires inverting the encoding for each component.  The input
                * is still converted to the sRGB encoding because this is a
                * reasonable approximate to the logarithmic curve of human
                * visual sensitivity, at least over the narrow range which PNG
                * represents.  Consequently 'G' is always sRGB encoded, while
                * 'A' is linear.  We need the linear background colors.
                */
               if (output_encoding == P_sRGB) /* else already linear */
               {
                  /* This may produce a value not exactly matching the
                   * background, but that's ok because these numbers are only
                   * used when alpha != 0
                   */
                  back_r = png_sRGB_table[back_r];
                  back_g = png_sRGB_table[back_g];
                  back_b = png_sRGB_table[back_b];
               }

               for (a=1; a<5; ++a)
               {
                  unsigned int g;

                  /* PNG_sRGB_FROM_LINEAR expects a 16-bit linear value scaled
                   * by an 8-bit alpha value (0..255).
                   */
                  png_uint_32 alpha = 51 * a;
                  png_uint_32 back_rx = (255-alpha) * back_r;
                  png_uint_32 back_gx = (255-alpha) * back_g;
                  png_uint_32 back_bx = (255-alpha) * back_b;

                  for (g=0; g<6; ++g)
                  {
                     png_uint_32 gray = png_sRGB_table[g*51] * alpha;

                     png_create_colormap_entry(display, i++,
                        PNG_sRGB_FROM_LINEAR(gray + back_rx),
                        PNG_sRGB_FROM_LINEAR(gray + back_gx),
                        PNG_sRGB_FROM_LINEAR(gray + back_bx), 255, P_sRGB);
                  }
               }

               cmap_entries = i;
               output_processing = PNG_CMAP_GA;
            }
         }
         break;

      case PNG_COLOR_TYPE_RGB:
      case PNG_COLOR_TYPE_RGB_ALPHA:
         /* Exclude the case where the output is gray; we can always handle this
          * with the cases above.
          */
         if ((output_format & PNG_FORMAT_FLAG_COLOR) == 0)
         {
            /* The color-map will be grayscale, so we may as well convert the
             * input RGB values to a simple grayscale and use the grayscale
             * code above.
             *
             * NOTE: calling this apparently damages the recognition of the
             * transparent color in background color handling; call
             * png_set_tRNS_to_alpha before png_set_background_fixed.
             */
            png_set_rgb_to_gray_fixed(png_ptr, PNG_ERROR_ACTION_NONE, -1,
               -1);
            data_encoding = P_sRGB;

            /* The output will now be one or two 8-bit gray or gray+alpha
             * channels.  The more complex case arises when the input has alpha.
             */
            if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
               png_ptr->num_trans > 0) &&
               (output_format & PNG_FORMAT_FLAG_ALPHA) != 0)
            {
               /* Both input and output have an alpha channel, so no background
                * processing is required; just map the GA bytes to the right
                * color-map entry.
                */
               expand_tRNS = 1;

               if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
                  png_error(png_ptr, "rgb[ga] color-map: too few entries");

               cmap_entries = make_ga_colormap(display);
               background_index = PNG_CMAP_GA_BACKGROUND;
               output_processing = PNG_CMAP_GA;
            }

            else
            {
               /* Either the input or the output has no alpha channel, so there
                * will be no non-opaque pixels in the color-map; it will just be
                * grayscale.
                */
               if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
                  png_error(png_ptr, "rgb[gray] color-map: too few entries");

               /* Ideally this code would use libpng to do the gamma correction,
                * but if an input alpha channel is to be removed we will hit the
                * libpng bug in gamma+compose+rgb-to-gray (the double gamma
                * correction bug).  Fix this by dropping the gamma correction in
                * this case and doing it in the palette; this will result in
                * duplicate palette entries, but that's better than the
                * alternative of double gamma correction.
                */
               if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
                  png_ptr->num_trans > 0) &&
                  png_gamma_not_sRGB(png_ptr->colorspace.gamma))
               {
                  cmap_entries = make_gray_file_colormap(display);
                  data_encoding = P_FILE;
               }

               else
                  cmap_entries = make_gray_colormap(display);

               /* But if the input has alpha or transparency it must be removed
                */
               if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
                  png_ptr->num_trans > 0)
               {
                  png_color_16 c;
                  png_uint_32 gray = back_g;

                  /* We need to ensure that the application background exists in
                   * the colormap and that completely transparent pixels map to
                   * it.  Achieve this simply by ensuring that the entry
                   * selected for the background really is the background color.
                   */
                  if (data_encoding == P_FILE) /* from the fixup above */
                  {
                     /* The app supplied a gray which is in output_encoding, we
                      * need to convert it to a value of the input (P_FILE)
                      * encoding then set this palette entry to the required
                      * output encoding.
                      */
                     if (output_encoding == P_sRGB)
                        gray = png_sRGB_table[gray]; /* now P_LINEAR */

                     gray = PNG_DIV257(png_gamma_16bit_correct(gray,
                        png_ptr->colorspace.gamma)); /* now P_FILE */

                     /* And make sure the corresponding palette entry contains
                      * exactly the required sRGB value.
                      */
                     png_create_colormap_entry(display, gray, back_g, back_g,
                        back_g, 0/*unused*/, output_encoding);
                  }

                  else if (output_encoding == P_LINEAR)
                  {
                     gray = PNG_sRGB_FROM_LINEAR(gray * 255);

                     /* And make sure the corresponding palette entry matches.
                      */
                     png_create_colormap_entry(display, gray, back_g, back_g,
                        back_g, 0/*unused*/, P_LINEAR);
                  }

                  /* The background passed to libpng, however, must be the
                   * output (normally sRGB) value.
                   */
                  c.index = 0; /*unused*/
                  c.gray = c.red = c.green = c.blue = (png_uint_16)gray;

                  /* NOTE: the following is apparently a bug in libpng. Without
                   * it the transparent color recognition in
                   * png_set_background_fixed seems to go wrong.
                   */
                  expand_tRNS = 1;
                  png_set_background_fixed(png_ptr, &c,
                     PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                     0/*gamma: not used*/);
               }

               output_processing = PNG_CMAP_NONE;
            }
         }

         else /* output is color */
         {
            /* We could use png_quantize here so long as there is no transparent
             * color or alpha; png_quantize ignores alpha.  Easier overall just
             * to do it once and using PNG_DIV51 on the 6x6x6 reduced RGB cube.
             * Consequently we always want libpng to produce sRGB data.
             */
            data_encoding = P_sRGB;

            /* Is there any transparency or alpha? */
            if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
               png_ptr->num_trans > 0)
            {
               /* Is there alpha in the output too?  If so all four channels are
                * processed into a special RGB cube with alpha support.
                */
               if (output_format & PNG_FORMAT_FLAG_ALPHA)
               {
                  png_uint_32 r;

                  if (PNG_RGB_COLORMAP_ENTRIES+1+27 > image->colormap_entries)
                     png_error(png_ptr, "rgb+alpha color-map: too few entries");

                  cmap_entries = make_rgb_colormap(display);

                  /* Add a transparent entry. */
                  png_create_colormap_entry(display, cmap_entries, 255, 255,
                     255, 0, P_sRGB);

                  /* This is stored as the background index for the processing
                   * algorithm.
                   */
                  background_index = cmap_entries++;

                  /* Add 27 r,g,b entries each with alpha 0.5. */
                  for (r=0; r<256; r = (r << 1) | 0x7f)
                  {
                     png_uint_32 g;

                     for (g=0; g<256; g = (g << 1) | 0x7f)
                     {
                        png_uint_32 b;

                        /* This generates components with the values 0, 127 and
                         * 255
                         */
                        for (b=0; b<256; b = (b << 1) | 0x7f)
                           png_create_colormap_entry(display, cmap_entries++,
                              r, g, b, 128, P_sRGB);
                     }
                  }

                  expand_tRNS = 1;
                  output_processing = PNG_CMAP_RGB_ALPHA;
               }

               else
               {
                  /* Alpha/transparency must be removed.  The background must
                   * exist in the color map (achieved by setting adding it after
                   * the 666 color-map).  If the standard processing code will
                   * pick up this entry automatically that's all that is
                   * required; libpng can be called to do the background
                   * processing.
                   */
                  unsigned int sample_size =
                     PNG_IMAGE_SAMPLE_SIZE(output_format);
                  png_uint_32 r, g, b; /* sRGB background */

                  if (PNG_RGB_COLORMAP_ENTRIES+1+27 > image->colormap_entries)
                     png_error(png_ptr, "rgb-alpha color-map: too few entries");

                  cmap_entries = make_rgb_colormap(display);

                  png_create_colormap_entry(display, cmap_entries, back_r,
                        back_g, back_b, 0/*unused*/, output_encoding);

                  if (output_encoding == P_LINEAR)
                  {
                     r = PNG_sRGB_FROM_LINEAR(back_r * 255);
                     g = PNG_sRGB_FROM_LINEAR(back_g * 255);
                     b = PNG_sRGB_FROM_LINEAR(back_b * 255);
                  }

                  else
                  {
                     r = back_r;
                     g = back_g;
                     b = back_g;
                  }

                  /* Compare the newly-created color-map entry with the one the
                   * PNG_CMAP_RGB algorithm will use.  If the two entries don't
                   * match, add the new one and set this as the background
                   * index.
                   */
                  if (memcmp((png_const_bytep)display->colormap +
                        sample_size * cmap_entries,
                     (png_const_bytep)display->colormap +
                        sample_size * PNG_RGB_INDEX(r,g,b),
                     sample_size) != 0)
                  {
                     /* The background color must be added. */
                     background_index = cmap_entries++;

                     /* Add 27 r,g,b entries each with created by composing with
                      * the background at alpha 0.5.
                      */
                     for (r=0; r<256; r = (r << 1) | 0x7f)
                     {
                        for (g=0; g<256; g = (g << 1) | 0x7f)
                        {
                           /* This generates components with the values 0, 127
                            * and 255
                            */
                           for (b=0; b<256; b = (b << 1) | 0x7f)
                              png_create_colormap_entry(display, cmap_entries++,
                                 png_colormap_compose(display, r, P_sRGB, 128,
                                    back_r, output_encoding),
                                 png_colormap_compose(display, g, P_sRGB, 128,
                                    back_g, output_encoding),
                                 png_colormap_compose(display, b, P_sRGB, 128,
                                    back_b, output_encoding),
                                 0/*unused*/, output_encoding);
                        }
                     }

                     expand_tRNS = 1;
                     output_processing = PNG_CMAP_RGB_ALPHA;
                  }

                  else /* background color is in the standard color-map */
                  {
                     png_color_16 c;

                     c.index = 0; /*unused*/
                     c.red = (png_uint_16)back_r;
                     c.gray = c.green = (png_uint_16)back_g;
                     c.blue = (png_uint_16)back_b;

                     png_set_background_fixed(png_ptr, &c,
                        PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                        0/*gamma: not used*/);

                     output_processing = PNG_CMAP_RGB;
                  }
               }
            }

            else /* no alpha or transparency in the input */
            {
               /* Alpha in the output is irrelevant, simply map the opaque input
                * pixels to the 6x6x6 color-map.
                */
               if (PNG_RGB_COLORMAP_ENTRIES > image->colormap_entries)
                  png_error(png_ptr, "rgb color-map: too few entries");

               cmap_entries = make_rgb_colormap(display);
               output_processing = PNG_CMAP_RGB;
            }
         }
         break;

      case PNG_COLOR_TYPE_PALETTE:
         /* It's already got a color-map.  It may be necessary to eliminate the
          * tRNS entries though.
          */
         {
            unsigned int num_trans = png_ptr->num_trans;
            png_const_bytep trans = num_trans > 0 ? png_ptr->trans_alpha : NULL;
            png_const_colorp colormap = png_ptr->palette;
            const int do_background = trans != NULL &&
               (output_format & PNG_FORMAT_FLAG_ALPHA) == 0;
            unsigned int i;

            /* Just in case: */
            if (trans == NULL)
               num_trans = 0;

            output_processing = PNG_CMAP_NONE;
            data_encoding = P_FILE; /* Don't change from color-map indicies */
            cmap_entries = png_ptr->num_palette;
            if (cmap_entries > 256)
               cmap_entries = 256;

            if (cmap_entries > image->colormap_entries)
               png_error(png_ptr, "palette color-map: too few entries");

            for (i=0; i < cmap_entries; ++i)
            {
               if (do_background && i < num_trans && trans[i] < 255)
               {
                  if (trans[i] == 0)
                     png_create_colormap_entry(display, i, back_r, back_g,
                        back_b, 0, output_encoding);

                  else
                  {
                     /* Must compose the PNG file color in the color-map entry
                      * on the sRGB color in 'back'.
                      */
                     png_create_colormap_entry(display, i,
                        png_colormap_compose(display, colormap[i].red, P_FILE,
                           trans[i], back_r, output_encoding),
                        png_colormap_compose(display, colormap[i].green, P_FILE,
                           trans[i], back_g, output_encoding),
                        png_colormap_compose(display, colormap[i].blue, P_FILE,
                           trans[i], back_b, output_encoding),
                        output_encoding == P_LINEAR ? trans[i] * 257U :
                           trans[i],
                        output_encoding);
                  }
               }

               else
                  png_create_colormap_entry(display, i, colormap[i].red,
                     colormap[i].green, colormap[i].blue,
                     i < num_trans ? trans[i] : 255U, P_FILE/*8-bit*/);
            }

            /* The PNG data may have indicies packed in fewer than 8 bits, it
             * must be expanded if so.
             */
            if (png_ptr->bit_depth < 8)
               png_set_packing(png_ptr);
         }
         break;

      default:
         png_error(png_ptr, "invalid PNG color type");
         /*NOT REACHED*/
         break;
   }

   /* Now deal with the output processing */
   if (expand_tRNS && png_ptr->num_trans > 0 &&
      (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) == 0)
      png_set_tRNS_to_alpha(png_ptr);

   switch (data_encoding)
   {
      default:
         png_error(png_ptr, "bad data option (internal error)");
         break;

      case P_sRGB:
         /* Change to 8-bit sRGB */
         png_set_alpha_mode_fixed(png_ptr, PNG_ALPHA_PNG, PNG_GAMMA_sRGB);
         /* FALL THROUGH */

      case P_FILE:
         if (png_ptr->bit_depth > 8)
            png_set_scale_16(png_ptr);
         break;
   }

   if (cmap_entries > 256 || cmap_entries > image->colormap_entries)
      png_error(png_ptr, "color map overflow (BAD internal error)");

   image->colormap_entries = cmap_entries;

   /* Double check using the recorded background index */
   switch (output_processing)
   {
      case PNG_CMAP_NONE:
         if (background_index != PNG_CMAP_NONE_BACKGROUND)
            goto bad_background;
         break;

      case PNG_CMAP_GA:
         if (background_index != PNG_CMAP_GA_BACKGROUND)
            goto bad_background;
         break;

      case PNG_CMAP_TRANS:
         if (background_index >= cmap_entries ||
            background_index != PNG_CMAP_TRANS_BACKGROUND)
            goto bad_background;
         break;

      case PNG_CMAP_RGB:
         if (background_index != PNG_CMAP_RGB_BACKGROUND)
            goto bad_background;
         break;

      case PNG_CMAP_RGB_ALPHA:
         if (background_index != PNG_CMAP_RGB_ALPHA_BACKGROUND)
            goto bad_background;
         break;

      default:
         png_error(png_ptr, "bad processing option (internal error)");

      bad_background:
         png_error(png_ptr, "bad background index (internal error)");
   }

   display->colormap_processing = output_processing;

   return 1/*ok*/;
}

/* The final part of the color-map read called from png_image_finish_read. */
static int
png_image_read_and_map(png_voidp argument)
{
   png_image_read_control *display = png_voidcast(png_image_read_control*,
      argument);
   png_imagep image = display->image;
   png_structrp png_ptr = image->opaque->png_ptr;
   int passes;

   /* Called when the libpng data must be transformed into the color-mapped
    * form.  There is a local row buffer in display->local and this routine must
    * do the interlace handling.
    */
   switch (png_ptr->interlaced)
   {
      case PNG_INTERLACE_NONE:
         passes = 1;
         break;

      case PNG_INTERLACE_ADAM7:
         passes = PNG_INTERLACE_ADAM7_PASSES;
         break;

      default:
         png_error(png_ptr, "unknown interlace type");
   }

   {
      png_uint_32  height = image->height;
      png_uint_32  width = image->width;
      int          proc = display->colormap_processing;
      png_bytep    first_row = png_voidcast(png_bytep, display->first_row);
      ptrdiff_t    step_row = display->row_bytes;
      int pass;

      for (pass = 0; pass < passes; ++pass)
      {
         unsigned int     startx, stepx, stepy;
         png_uint_32      y;

         if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
         {
            /* The row may be empty for a short image: */
            if (PNG_PASS_COLS(width, pass) == 0)
               continue;

            startx = PNG_PASS_START_COL(pass);
            stepx = PNG_PASS_COL_OFFSET(pass);
            y = PNG_PASS_START_ROW(pass);
            stepy = PNG_PASS_ROW_OFFSET(pass);
         }

         else
         {
            y = 0;
            startx = 0;
            stepx = stepy = 1;
         }

         for (; y<height; y += stepy)
         {
            png_bytep inrow = png_voidcast(png_bytep, display->local_row);
            png_bytep outrow = first_row + y * step_row;
            png_const_bytep end_row = outrow + width;

            /* Read read the libpng data into the temporary buffer. */
            png_read_row(png_ptr, inrow, NULL);

            /* Now process the row according to the processing option, note
             * that the caller verifies that the format of the libpng output
             * data is as required.
             */
            outrow += startx;
            switch (proc)
            {
               case PNG_CMAP_GA:
                  for (; outrow < end_row; outrow += stepx)
                  {
                     /* The data is always in the PNG order */
                     unsigned int gray = *inrow++;
                     unsigned int alpha = *inrow++;
                     unsigned int entry;

                     /* NOTE: this code is copied as a comment in
                      * make_ga_colormap above.  Please update the
                      * comment if you change this code!
                      */
                     if (alpha > 229) /* opaque */
                     {
                        entry = (231 * gray + 128) >> 8;
                     }
                     else if (alpha < 26) /* transparent */
                     {
                        entry = 231;
                     }
                     else /* partially opaque */
                     {
                        entry = 226 + 6 * PNG_DIV51(alpha) + PNG_DIV51(gray);
                     }

                     *outrow = (png_byte)entry;
                  }
                  break;

               case PNG_CMAP_TRANS:
                  for (; outrow < end_row; outrow += stepx)
                  {
                     png_byte gray = *inrow++;
                     png_byte alpha = *inrow++;

                     if (alpha == 0)
                        *outrow = PNG_CMAP_TRANS_BACKGROUND;

                     else if (gray != PNG_CMAP_TRANS_BACKGROUND)
                        *outrow = gray;

                     else
                        *outrow = (png_byte)(PNG_CMAP_TRANS_BACKGROUND+1);
                  }
                  break;

               case PNG_CMAP_RGB:
                  for (; outrow < end_row; outrow += stepx)
                  {
                     *outrow = PNG_RGB_INDEX(inrow[0], inrow[1], inrow[2]);
                     inrow += 3;
                  }
                  break;

               case PNG_CMAP_RGB_ALPHA:
                  for (; outrow < end_row; outrow += stepx)
                  {
                     unsigned int alpha = inrow[3];

                     /* Because the alpha entries only hold alpha==0.5 values
                      * split the processing at alpha==0.25 (64) and 0.75
                      * (196).
                      */

                     if (alpha >= 196)
                        *outrow = PNG_RGB_INDEX(inrow[0], inrow[1],
                           inrow[2]);

                     else if (alpha < 64)
                        *outrow = PNG_CMAP_RGB_ALPHA_BACKGROUND;

                     else
                     {
                        /* Likewise there are three entries for each of r, g
                         * and b.  We could select the entry by popcount on
                         * the top two bits on those architectures that
                         * support it, this is what the code below does,
                         * crudely.
                         */
                        unsigned int back_i = PNG_CMAP_RGB_ALPHA_BACKGROUND+1;

                        /* Here are how the values map:
                         *
                         * 0x00 .. 0x3f -> 0
                         * 0x40 .. 0xbf -> 1
                         * 0xc0 .. 0xff -> 2
                         *
                         * So, as above with the explicit alpha checks, the
                         * breakpoints are at 64 and 196.
                         */
                        if (inrow[0] & 0x80) back_i += 9; /* red */
                        if (inrow[0] & 0x40) back_i += 9;
                        if (inrow[0] & 0x80) back_i += 3; /* green */
                        if (inrow[0] & 0x40) back_i += 3;
                        if (inrow[0] & 0x80) back_i += 1; /* blue */
                        if (inrow[0] & 0x40) back_i += 1;

                        *outrow = (png_byte)back_i;
                     }

                     inrow += 4;
                  }
                  break;

               default:
                  break;
            }
         }
      }
   }

   return 1;
}

static int
png_image_read_colormapped(png_voidp argument)
{
   png_image_read_control *display = png_voidcast(png_image_read_control*,
      argument);
   png_imagep image = display->image;
   png_controlp control = image->opaque;
   png_structrp png_ptr = control->png_ptr;
   png_inforp info_ptr = control->info_ptr;

   int passes = 0; /* As a flag */

   PNG_SKIP_CHUNKS(png_ptr);

   /* Update the 'info' structure and make sure the result is as required; first
    * make sure to turn on the interlace handling if it will be required
    * (because it can't be turned on *after* the call to png_read_update_info!)
    */
   if (display->colormap_processing == PNG_CMAP_NONE)
      passes = png_set_interlace_handling(png_ptr);

   png_read_update_info(png_ptr, info_ptr);

   /* The expected output can be deduced from the colormap_processing option. */
   switch (display->colormap_processing)
   {
      case PNG_CMAP_NONE:
         /* Output must be one channel and one byte per pixel, the output
          * encoding can be anything.
          */
         if ((info_ptr->color_type == PNG_COLOR_TYPE_PALETTE ||
            info_ptr->color_type == PNG_COLOR_TYPE_GRAY) &&
            info_ptr->bit_depth == 8)
            break;

         goto bad_output;

      case PNG_CMAP_TRANS:
      case PNG_CMAP_GA:
         /* Output must be two channels and the 'G' one must be sRGB, the latter
          * can be checked with an exact number because it should have been set
          * to this number above!
          */
         if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY_ALPHA &&
            info_ptr->bit_depth == 8 &&
            png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
            image->colormap_entries == 256)
            break;

         goto bad_output;

      case PNG_CMAP_RGB:
         /* Output must be 8-bit sRGB encoded RGB */
         if (info_ptr->color_type == PNG_COLOR_TYPE_RGB &&
            info_ptr->bit_depth == 8 &&
            png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
            image->colormap_entries == 216)
            break;

         goto bad_output;

      case PNG_CMAP_RGB_ALPHA:
         /* Output must be 8-bit sRGB encoded RGBA */
         if (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA &&
            info_ptr->bit_depth == 8 &&
            png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
            image->colormap_entries == 244 /* 216 + 1 + 27 */)
            break;

         /* goto bad_output; */
         /* FALL THROUGH */

      default:
      bad_output:
         png_error(png_ptr, "bad color-map processing (internal error)");
   }

   /* Now read the rows.  Do this here if it is possible to read directly into
    * the output buffer, otherwise allocate a local row buffer of the maximum
    * size libpng requires and call the relevant processing routine safely.
    */
   {
      png_voidp first_row = display->buffer;
      ptrdiff_t row_bytes = display->row_stride;

      /* The following expression is designed to work correctly whether it gives
       * a signed or an unsigned result.
       */
      if (row_bytes < 0)
      {
         char *ptr = png_voidcast(char*, first_row);
         ptr += (image->height-1) * (-row_bytes);
         first_row = png_voidcast(png_voidp, ptr);
      }

      display->first_row = first_row;
      display->row_bytes = row_bytes;
   }

   if (passes == 0)
   {
      int result;
      png_voidp row = png_malloc(png_ptr, png_get_rowbytes(png_ptr, info_ptr));

      display->local_row = row;
      result = png_safe_execute(image, png_image_read_and_map, display);
      display->local_row = NULL;
      png_free(png_ptr, row);

      return result;
   }

   else
   {
      png_alloc_size_t row_bytes = display->row_bytes;

      while (--passes >= 0)
      {
         png_uint_32      y = image->height;
         png_bytep        row = png_voidcast(png_bytep, display->first_row);

         while (y-- > 0)
         {
            png_read_row(png_ptr, row, NULL);
            row += row_bytes;
         }
      }

      return 1;
   }
}

/* Just the row reading part of png_image_read. */
static int
png_image_read_composite(png_voidp argument)
{
   png_image_read_control *display = png_voidcast(png_image_read_control*,
      argument);
   png_imagep image = display->image;
   png_structrp png_ptr = image->opaque->png_ptr;
   int passes;

   switch (png_ptr->interlaced)
   {
      case PNG_INTERLACE_NONE:
         passes = 1;
         break;

      case PNG_INTERLACE_ADAM7:
         passes = PNG_INTERLACE_ADAM7_PASSES;
         break;

      default:
         png_error(png_ptr, "unknown interlace type");
   }

   {
      png_uint_32  height = image->height;
      png_uint_32  width = image->width;
      ptrdiff_t    step_row = display->row_bytes;
      unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) ? 3 : 1;
      int pass;

      for (pass = 0; pass < passes; ++pass)
      {
         unsigned int     startx, stepx, stepy;
         png_uint_32      y;

         if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
         {
            /* The row may be empty for a short image: */
            if (PNG_PASS_COLS(width, pass) == 0)
               continue;

            startx = PNG_PASS_START_COL(pass) * channels;
            stepx = PNG_PASS_COL_OFFSET(pass) * channels;
            y = PNG_PASS_START_ROW(pass);
            stepy = PNG_PASS_ROW_OFFSET(pass);
         }

         else
         {
            y = 0;
            startx = 0;
            stepx = channels;
            stepy = 1;
         }

         for (; y<height; y += stepy)
         {
            png_bytep inrow = png_voidcast(png_bytep, display->local_row);
            png_bytep outrow;
            png_const_bytep end_row;

            /* Read the row, which is packed: */
            png_read_row(png_ptr, inrow, NULL);

            outrow = png_voidcast(png_bytep, display->first_row);
            outrow += y * step_row;
            end_row = outrow + width * channels;

            /* Now do the composition on each pixel in this row. */
            outrow += startx;
            for (; outrow < end_row; outrow += stepx)
            {
               png_byte alpha = inrow[channels];

               if (alpha > 0) /* else no change to the output */
               {
                  unsigned int c;

                  for (c=0; c<channels; ++c)
                  {
                     png_uint_32 component = inrow[c];

                     if (alpha < 255) /* else just use component */
                     {
                        /* This is PNG_OPTIMIZED_ALPHA, the component value
                         * is a linear 8-bit value.  Combine this with the
                         * current outrow[c] value which is sRGB encoded.
                         * Arithmetic here is 16-bits to preserve the output
                         * values correctly.
                         */
                        component *= 257*255; /* =65535 */
                        component += (255-alpha)*png_sRGB_table[outrow[c]];

                        /* So 'component' is scaled by 255*65535 and is
                         * therefore appropriate for the sRGB to linear
                         * conversion table.
                         */
                        component = PNG_sRGB_FROM_LINEAR(component);
                     }

                     outrow[c] = (png_byte)component;
                  }
               }

               inrow += channels+1; /* components and alpha channel */
            }
         }
      }
   }

   return 1;
}

/* The do_local_background case; called when all the following transforms are to
 * be done:
 *
 * PNG_RGB_TO_GRAY
 * PNG_COMPOSITE
 * PNG_GAMMA
 *
 * This is a work-round for the fact that both the PNG_RGB_TO_GRAY and
 * PNG_COMPOSITE code performs gamma correction, so we get double gamma
 * correction.  The fix-up is to prevent the PNG_COMPOSITE operation happening
 * inside libpng, so this routine sees an 8 or 16-bit gray+alpha row and handles
 * the removal or pre-multiplication of the alpha channel.
 */
static int
png_image_read_background(png_voidp argument)
{
   png_image_read_control *display = png_voidcast(png_image_read_control*,
      argument);
   png_imagep image = display->image;
   png_structrp png_ptr = image->opaque->png_ptr;
   png_inforp info_ptr = image->opaque->info_ptr;
   png_uint_32 height = image->height;
   png_uint_32 width = image->width;
   int pass, passes;

   /* Double check the convoluted logic below.  We expect to get here with
    * libpng doing rgb to gray and gamma correction but background processing
    * left to the png_image_read_background function.  The rows libpng produce
    * might be 8 or 16-bit but should always have two channels; gray plus alpha.
    */
   if ((png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
      png_error(png_ptr, "lost rgb to gray");

   if ((png_ptr->transformations & PNG_COMPOSE) != 0)
      png_error(png_ptr, "unexpected compose");

   if (png_get_channels(png_ptr, info_ptr) != 2)
      png_error(png_ptr, "lost/gained channels");

   /* Expect the 8-bit case to always remove the alpha channel */
   if ((image->format & PNG_FORMAT_FLAG_LINEAR) == 0 &&
      (image->format & PNG_FORMAT_FLAG_ALPHA) != 0)
      png_error(png_ptr, "unexpected 8-bit transformation");

   switch (png_ptr->interlaced)
   {
      case PNG_INTERLACE_NONE:
         passes = 1;
         break;

      case PNG_INTERLACE_ADAM7:
         passes = PNG_INTERLACE_ADAM7_PASSES;
         break;

      default:
         png_error(png_ptr, "unknown interlace type");
   }

   /* Use direct access to info_ptr here because otherwise the simplified API
    * would require PNG_EASY_ACCESS_SUPPORTED (just for this.)  Note this is
    * checking the value after libpng expansions, not the original value in the
    * PNG.
    */
   switch (info_ptr->bit_depth)
   {
      default:
         png_error(png_ptr, "unexpected bit depth");
         break;

      case 8:
         /* 8-bit sRGB gray values with an alpha channel; the alpha channel is
          * to be removed by composing on a background: either the row if
          * display->background is NULL or display->background->green if not.
          * Unlike the code above ALPHA_OPTIMIZED has *not* been done.
          */
         {
            png_bytep first_row = png_voidcast(png_bytep, display->first_row);
            ptrdiff_t step_row = display->row_bytes;

            for (pass = 0; pass < passes; ++pass)
            {
               png_bytep        row = png_voidcast(png_bytep,
                                                   display->first_row);
               unsigned int     startx, stepx, stepy;
               png_uint_32      y;

               if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
               {
                  /* The row may be empty for a short image: */
                  if (PNG_PASS_COLS(width, pass) == 0)
                     continue;

                  startx = PNG_PASS_START_COL(pass);
                  stepx = PNG_PASS_COL_OFFSET(pass);
                  y = PNG_PASS_START_ROW(pass);
                  stepy = PNG_PASS_ROW_OFFSET(pass);
               }

               else
               {
                  y = 0;
                  startx = 0;
                  stepx = stepy = 1;
               }

               if (display->background == NULL)
               {
                  for (; y<height; y += stepy)
                  {
                     png_bytep inrow = png_voidcast(png_bytep,
                        display->local_row);
                     png_bytep outrow = first_row + y * step_row;
                     png_const_bytep end_row = outrow + width;

                     /* Read the row, which is packed: */
                     png_read_row(png_ptr, inrow, NULL);

                     /* Now do the composition on each pixel in this row. */
                     outrow += startx;
                     for (; outrow < end_row; outrow += stepx)
                     {
                        png_byte alpha = inrow[1];

                        if (alpha > 0) /* else no change to the output */
                        {
                           png_uint_32 component = inrow[0];

                           if (alpha < 255) /* else just use component */
                           {
                              /* Since PNG_OPTIMIZED_ALPHA was not set it is
                               * necessary to invert the sRGB transfer
                               * function and multiply the alpha out.
                               */
                              component = png_sRGB_table[component] * alpha;
                              component += png_sRGB_table[outrow[0]] *
                                 (255-alpha);
                              component = PNG_sRGB_FROM_LINEAR(component);
                           }

                           outrow[0] = (png_byte)component;
                        }

                        inrow += 2; /* gray and alpha channel */
                     }
                  }
               }

               else /* constant background value */
               {
                  png_byte background8 = display->background->green;
                  png_uint_16 background = png_sRGB_table[background8];

                  for (; y<height; y += stepy)
                  {
                     png_bytep inrow = png_voidcast(png_bytep,
                        display->local_row);
                     png_bytep outrow = first_row + y * step_row;
                     png_const_bytep end_row = outrow + width;

                     /* Read the row, which is packed: */
                     png_read_row(png_ptr, inrow, NULL);

                     /* Now do the composition on each pixel in this row. */
                     outrow += startx;
                     for (; outrow < end_row; outrow += stepx)
                     {
                        png_byte alpha = inrow[1];

                        if (alpha > 0) /* else use background */
                        {
                           png_uint_32 component = inrow[0];

                           if (alpha < 255) /* else just use component */
                           {
                              component = png_sRGB_table[component] * alpha;
                              component += background * (255-alpha);
                              component = PNG_sRGB_FROM_LINEAR(component);
                           }

                           outrow[0] = (png_byte)component;
                        }

                        else
                           outrow[0] = background8;

                        inrow += 2; /* gray and alpha channel */
                     }

                     row += display->row_bytes;
                  }
               }
            }
         }
         break;

      case 16:
         /* 16-bit linear with pre-multiplied alpha; the pre-multiplication must
          * still be done and, maybe, the alpha channel removed.  This code also
          * handles the alpha-first option.
          */
         {
            png_uint_16p first_row = png_voidcast(png_uint_16p,
               display->first_row);
            /* The division by two is safe because the caller passed in a
             * stride which was multiplied by 2 (below) to get row_bytes.
             */
            ptrdiff_t    step_row = display->row_bytes / 2;
            int preserve_alpha = (image->format & PNG_FORMAT_FLAG_ALPHA) != 0;
            unsigned int outchannels = 1+preserve_alpha;
            int swap_alpha = 0;

#           ifdef PNG_SIMPLIFIED_READ_AFIRST_SUPPORTED
               if (preserve_alpha && (image->format & PNG_FORMAT_FLAG_AFIRST))
                  swap_alpha = 1;
#           endif

            for (pass = 0; pass < passes; ++pass)
            {
               unsigned int     startx, stepx, stepy;
               png_uint_32      y;

               /* The 'x' start and step are adjusted to output components here.
                */
               if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
               {
                  /* The row may be empty for a short image: */
                  if (PNG_PASS_COLS(width, pass) == 0)
                     continue;

                  startx = PNG_PASS_START_COL(pass) * outchannels;
                  stepx = PNG_PASS_COL_OFFSET(pass) * outchannels;
                  y = PNG_PASS_START_ROW(pass);
                  stepy = PNG_PASS_ROW_OFFSET(pass);
               }

               else
               {
                  y = 0;
                  startx = 0;
                  stepx = outchannels;
                  stepy = 1;
               }

               for (; y<height; y += stepy)
               {
                  png_const_uint_16p inrow;
                  png_uint_16p outrow = first_row + y*step_row;
                  png_uint_16p end_row = outrow + width * outchannels;

                  /* Read the row, which is packed: */
                  png_read_row(png_ptr, png_voidcast(png_bytep,
                     display->local_row), NULL);
                  inrow = png_voidcast(png_const_uint_16p, display->local_row);

                  /* Now do the pre-multiplication on each pixel in this row.
                   */
                  outrow += startx;
                  for (; outrow < end_row; outrow += stepx)
                  {
                     png_uint_32 component = inrow[0];
                     png_uint_16 alpha = inrow[1];

                     if (alpha > 0) /* else 0 */
                     {
                        if (alpha < 65535) /* else just use component */
                        {
                           component *= alpha;
                           component += 32767;
                           component /= 65535;
                        }
                     }

                     else
                        component = 0;

                     outrow[swap_alpha] = (png_uint_16)component;
                     if (preserve_alpha)
                        outrow[1 ^ swap_alpha] = alpha;

                     inrow += 2; /* components and alpha channel */
                  }
               }
            }
         }
         break;
   }

   return 1;
}

/* The guts of png_image_finish_read as a png_safe_execute callback. */
static int
png_image_read_direct(png_voidp argument)
{
   png_image_read_control *display = png_voidcast(png_image_read_control*,
      argument);
   png_imagep image = display->image;
   png_structrp png_ptr = image->opaque->png_ptr;
   png_inforp info_ptr = image->opaque->info_ptr;

   png_uint_32 format = image->format;
   int linear = (format & PNG_FORMAT_FLAG_LINEAR) != 0;
   int do_local_compose = 0;
   int do_local_background = 0; /* to avoid double gamma correction bug */
   int passes = 0;

   /* Add transforms to ensure the correct output format is produced then check
    * that the required implementation support is there.  Always expand; always
    * need 8 bits minimum, no palette and expanded tRNS.
    */
   png_set_expand(png_ptr);

   /* Now check the format to see if it was modified. */
   {
      png_uint_32 base_format = png_image_format(png_ptr) &
         ~PNG_FORMAT_FLAG_COLORMAP /* removed by png_set_expand */;
      png_uint_32 change = format ^ base_format;
      png_fixed_point output_gamma;
      int mode; /* alpha mode */

      /* Do this first so that we have a record if rgb to gray is happening. */
      if (change & PNG_FORMAT_FLAG_COLOR)
      {
         /* gray<->color transformation required. */
         if (format & PNG_FORMAT_FLAG_COLOR)
            png_set_gray_to_rgb(png_ptr);

         else
         {
            /* libpng can't do both rgb to gray and
             * background/pre-multiplication if there is also significant gamma
             * correction, because both operations require linear colors and
             * the code only supports one transform doing the gamma correction.
             * Handle this by doing the pre-multiplication or background
             * operation in this code, if necessary.
             *
             * TODO: fix this by rewriting pngrtran.c (!)
             *
             * For the moment (given that fixing this in pngrtran.c is an
             * enormous change) 'do_local_background' is used to indicate that
             * the problem exists.
             */
            if (base_format & PNG_FORMAT_FLAG_ALPHA)
               do_local_background = 1/*maybe*/;

            png_set_rgb_to_gray_fixed(png_ptr, PNG_ERROR_ACTION_NONE,
               PNG_RGB_TO_GRAY_DEFAULT, PNG_RGB_TO_GRAY_DEFAULT);
         }

         change &= ~PNG_FORMAT_FLAG_COLOR;
      }

      /* Set the gamma appropriately, linear for 16-bit input, sRGB otherwise.
       */
      {
         png_fixed_point input_gamma_default;

         if ((base_format & PNG_FORMAT_FLAG_LINEAR) &&
            (image->flags & PNG_IMAGE_FLAG_16BIT_sRGB) == 0)
            input_gamma_default = PNG_GAMMA_LINEAR;
         else
            input_gamma_default = PNG_DEFAULT_sRGB;

         /* Call png_set_alpha_mode to set the default for the input gamma; the
          * output gamma is set by a second call below.
          */
         png_set_alpha_mode_fixed(png_ptr, PNG_ALPHA_PNG, input_gamma_default);
      }

      if (linear)
      {
         /* If there *is* an alpha channel in the input it must be multiplied
          * out; use PNG_ALPHA_STANDARD, otherwise just use PNG_ALPHA_PNG.
          */
         if (base_format & PNG_FORMAT_FLAG_ALPHA)
            mode = PNG_ALPHA_STANDARD; /* associated alpha */

         else
            mode = PNG_ALPHA_PNG;

         output_gamma = PNG_GAMMA_LINEAR;
      }

      else
      {
         mode = PNG_ALPHA_PNG;
         output_gamma = PNG_DEFAULT_sRGB;
      }

      /* If 'do_local_background' is set check for the presence of gamma
       * correction; this is part of the work-round for the libpng bug
       * described above.
       *
       * TODO: fix libpng and remove this.
       */
      if (do_local_background)
      {
         png_fixed_point gtest;

         /* This is 'png_gamma_threshold' from pngrtran.c; the test used for
          * gamma correction, the screen gamma hasn't been set on png_struct
          * yet; it's set below.  png_struct::gamma, however, is set to the
          * final value.
          */
         if (png_muldiv(&gtest, output_gamma, png_ptr->colorspace.gamma,
               PNG_FP_1) && !png_gamma_significant(gtest))
            do_local_background = 0;

         else if (mode == PNG_ALPHA_STANDARD)
         {
            do_local_background = 2/*required*/;
            mode = PNG_ALPHA_PNG; /* prevent libpng doing it */
         }

         /* else leave as 1 for the checks below */
      }

      /* If the bit-depth changes then handle that here. */
      if (change & PNG_FORMAT_FLAG_LINEAR)
      {
         if (linear /*16-bit output*/)
            png_set_expand_16(png_ptr);

         else /* 8-bit output */
            png_set_scale_16(png_ptr);

         change &= ~PNG_FORMAT_FLAG_LINEAR;
      }

      /* Now the background/alpha channel changes. */
      if (change & PNG_FORMAT_FLAG_ALPHA)
      {
         /* Removing an alpha channel requires composition for the 8-bit
          * formats; for the 16-bit it is already done, above, by the
          * pre-multiplication and the channel just needs to be stripped.
          */
         if (base_format & PNG_FORMAT_FLAG_ALPHA)
         {
            /* If RGB->gray is happening the alpha channel must be left and the
             * operation completed locally.
             *
             * TODO: fix libpng and remove this.
             */
            if (do_local_background)
               do_local_background = 2/*required*/;

            /* 16-bit output: just remove the channel */
            else if (linear) /* compose on black (well, pre-multiply) */
               png_set_strip_alpha(png_ptr);

            /* 8-bit output: do an appropriate compose */
            else if (display->background != NULL)
            {
               png_color_16 c;

               c.index = 0; /*unused*/
               c.red = display->background->red;
               c.green = display->background->green;
               c.blue = display->background->blue;
               c.gray = display->background->green;

               /* This is always an 8-bit sRGB value, using the 'green' channel
                * for gray is much better than calculating the luminance here;
                * we can get off-by-one errors in that calculation relative to
                * the app expectations and that will show up in transparent
                * pixels.
                */
               png_set_background_fixed(png_ptr, &c,
                  PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                  0/*gamma: not used*/);
            }

            else /* compose on row: implemented below. */
            {
               do_local_compose = 1;
               /* This leaves the alpha channel in the output, so it has to be
                * removed by the code below.  Set the encoding to the 'OPTIMIZE'
                * one so the code only has to hack on the pixels that require
                * composition.
                */
               mode = PNG_ALPHA_OPTIMIZED;
            }
         }

         else /* output needs an alpha channel */
         {
            /* This is tricky because it happens before the swap operation has
             * been accomplished; however, the swap does *not* swap the added
             * alpha channel (weird API), so it must be added in the correct
             * place.
             */
            png_uint_32 filler; /* opaque filler */
            int where;

            if (linear)
               filler = 65535;

            else
               filler = 255;

#           ifdef PNG_FORMAT_AFIRST_SUPPORTED
               if (format & PNG_FORMAT_FLAG_AFIRST)
               {
                  where = PNG_FILLER_BEFORE;
                  change &= ~PNG_FORMAT_FLAG_AFIRST;
               }

               else
#           endif
               where = PNG_FILLER_AFTER;

            png_set_add_alpha(png_ptr, filler, where);
         }

         /* This stops the (irrelevant) call to swap_alpha below. */
         change &= ~PNG_FORMAT_FLAG_ALPHA;
      }

      /* Now set the alpha mode correctly; this is always done, even if there is
       * no alpha channel in either the input or the output because it correctly
       * sets the output gamma.
       */
      png_set_alpha_mode_fixed(png_ptr, mode, output_gamma);

#     ifdef PNG_FORMAT_BGR_SUPPORTED
         if (change & PNG_FORMAT_FLAG_BGR)
         {
            /* Check only the output format; PNG is never BGR; don't do this if
             * the output is gray, but fix up the 'format' value in that case.
             */
            if (format & PNG_FORMAT_FLAG_COLOR)
               png_set_bgr(png_ptr);

            else
               format &= ~PNG_FORMAT_FLAG_BGR;

            change &= ~PNG_FORMAT_FLAG_BGR;
         }
#     endif

#     ifdef PNG_FORMAT_AFIRST_SUPPORTED
         if (change & PNG_FORMAT_FLAG_AFIRST)
         {
            /* Only relevant if there is an alpha channel - it's particularly
             * important to handle this correctly because do_local_compose may
             * be set above and then libpng will keep the alpha channel for this
             * code to remove.
             */
            if (format & PNG_FORMAT_FLAG_ALPHA)
            {
               /* Disable this if doing a local background,
                * TODO: remove this when local background is no longer required.
                */
               if (do_local_background != 2)
                  png_set_swap_alpha(png_ptr);
            }

            else
               format &= ~PNG_FORMAT_FLAG_AFIRST;

            change &= ~PNG_FORMAT_FLAG_AFIRST;
         }
#     endif

      /* If the *output* is 16-bit then we need to check for a byte-swap on this
       * architecture.
       */
      if (linear)
      {
         PNG_CONST png_uint_16 le = 0x0001;

         if (*(png_const_bytep)&le)
            png_set_swap(png_ptr);
      }

      /* If change is not now 0 some transformation is missing - error out. */
      if (change)
         png_error(png_ptr, "png_read_image: unsupported transformation");
   }

   PNG_SKIP_CHUNKS(png_ptr);

   /* Update the 'info' structure and make sure the result is as required; first
    * make sure to turn on the interlace handling if it will be required
    * (because it can't be turned on *after* the call to png_read_update_info!)
    *
    * TODO: remove the do_local_background fixup below.
    */
   if (!do_local_compose && do_local_background != 2)
      passes = png_set_interlace_handling(png_ptr);

   png_read_update_info(png_ptr, info_ptr);

   {
      png_uint_32 info_format = 0;

      if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
         info_format |= PNG_FORMAT_FLAG_COLOR;

      if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
      {
         /* do_local_compose removes this channel below. */
         if (!do_local_compose)
         {
            /* do_local_background does the same if required. */
            if (do_local_background != 2 ||
               (format & PNG_FORMAT_FLAG_ALPHA) != 0)
               info_format |= PNG_FORMAT_FLAG_ALPHA;
         }
      }

      else if (do_local_compose) /* internal error */
         png_error(png_ptr, "png_image_read: alpha channel lost");

      if (info_ptr->bit_depth == 16)
         info_format |= PNG_FORMAT_FLAG_LINEAR;

#     ifdef PNG_FORMAT_BGR_SUPPORTED
         if (png_ptr->transformations & PNG_BGR)
            info_format |= PNG_FORMAT_FLAG_BGR;
#     endif

#     ifdef PNG_FORMAT_AFIRST_SUPPORTED
         if (do_local_background == 2)
         {
            if (format & PNG_FORMAT_FLAG_AFIRST)
               info_format |= PNG_FORMAT_FLAG_AFIRST;
         }

         if ((png_ptr->transformations & PNG_SWAP_ALPHA) != 0 ||
            ((png_ptr->transformations & PNG_ADD_ALPHA) != 0 &&
            (png_ptr->flags & PNG_FLAG_FILLER_AFTER) == 0))
         {
            if (do_local_background == 2)
               png_error(png_ptr, "unexpected alpha swap transformation");

            info_format |= PNG_FORMAT_FLAG_AFIRST;
         }
#     endif

      /* This is actually an internal error. */
      if (info_format != format)
         png_error(png_ptr, "png_read_image: invalid transformations");
   }

   /* Now read the rows.  If do_local_compose is set then it is necessary to use
    * a local row buffer.  The output will be GA, RGBA or BGRA and must be
    * converted to G, RGB or BGR as appropriate.  The 'local_row' member of the
    * display acts as a flag.
    */
   {
      png_voidp first_row = display->buffer;
      ptrdiff_t row_bytes = display->row_stride;

      if (linear)
         row_bytes *= 2;

      /* The following expression is designed to work correctly whether it gives
       * a signed or an unsigned result.
       */
      if (row_bytes < 0)
      {
         char *ptr = png_voidcast(char*, first_row);
         ptr += (image->height-1) * (-row_bytes);
         first_row = png_voidcast(png_voidp, ptr);
      }

      display->first_row = first_row;
      display->row_bytes = row_bytes;
   }

   if (do_local_compose)
   {
      int result;
      png_voidp row = png_malloc(png_ptr, png_get_rowbytes(png_ptr, info_ptr));

      display->local_row = row;
      result = png_safe_execute(image, png_image_read_composite, display);
      display->local_row = NULL;
      png_free(png_ptr, row);

      return result;
   }

   else if (do_local_background == 2)
   {
      int result;
      png_voidp row = png_malloc(png_ptr, png_get_rowbytes(png_ptr, info_ptr));

      display->local_row = row;
      result = png_safe_execute(image, png_image_read_background, display);
      display->local_row = NULL;
      png_free(png_ptr, row);

      return result;
   }

   else
   {
      png_alloc_size_t row_bytes = display->row_bytes;

      while (--passes >= 0)
      {
         png_uint_32      y = image->height;
         png_bytep        row = png_voidcast(png_bytep, display->first_row);

         while (y-- > 0)
         {
            png_read_row(png_ptr, row, NULL);
            row += row_bytes;
         }
      }

      return 1;
   }
}

int PNGAPI
png_image_finish_read(png_imagep image, png_const_colorp background,
   void *buffer, png_int_32 row_stride, void *colormap)
{
   if (image != NULL && image->version == PNG_IMAGE_VERSION)
   {
      png_uint_32 check;

      if (row_stride == 0)
         row_stride = PNG_IMAGE_ROW_STRIDE(*image);

      if (row_stride < 0)
         check = -row_stride;

      else
         check = row_stride;

      if (image->opaque != NULL && buffer != NULL &&
         check >= PNG_IMAGE_ROW_STRIDE(*image))
      {
         if ((image->format & PNG_FORMAT_FLAG_COLORMAP) == 0 ||
            (image->colormap_entries > 0 && colormap != NULL))
         {
            int result;
            png_image_read_control display;

            memset(&display, 0, (sizeof display));
            display.image = image;
            display.buffer = buffer;
            display.row_stride = row_stride;
            display.colormap = colormap;
            display.background = background;
            display.local_row = NULL;

            /* Choose the correct 'end' routine; for the color-map case all the
             * setup has already been done.
             */
            if (image->format & PNG_FORMAT_FLAG_COLORMAP)
               result =
                  png_safe_execute(image, png_image_read_colormap, &display) &&
                  png_safe_execute(image, png_image_read_colormapped, &display);

            else
               result =
                  png_safe_execute(image, png_image_read_direct, &display);

            png_image_free(image);
            return result;
         }

         else
            return png_image_error(image,
               "png_image_finish_read[color-map]: no color-map");
      }

      else
         return png_image_error(image,
            "png_image_finish_read: invalid argument");
   }

   else if (image != NULL)
      return png_image_error(image,
         "png_image_finish_read: damaged PNG_IMAGE_VERSION");

   return 0;
}

#endif /* PNG_SIMPLIFIED_READ_SUPPORTED */
#endif /* PNG_READ_SUPPORTED */