diff options
Diffstat (limited to 'plugins/AdvaImg/src/LibJPEG/usage.txt')
| -rw-r--r-- | plugins/AdvaImg/src/LibJPEG/usage.txt | 47 |
1 files changed, 37 insertions, 10 deletions
diff --git a/plugins/AdvaImg/src/LibJPEG/usage.txt b/plugins/AdvaImg/src/LibJPEG/usage.txt index c8ea77cd26..ca9f7d74a4 100644 --- a/plugins/AdvaImg/src/LibJPEG/usage.txt +++ b/plugins/AdvaImg/src/LibJPEG/usage.txt @@ -158,10 +158,10 @@ file size is about the same --- often a little smaller. Switches for advanced users:
- -arithmetic Use arithmetic coding. CAUTION: arithmetic coded JPEG
- is not yet widely implemented, so many decoders will
- be unable to view an arithmetic coded JPEG file at
- all.
+ -arithmetic Use arithmetic coding.
+ CAUTION: arithmetic coded JPEG is not yet widely
+ implemented, so many decoders will be unable to
+ view an arithmetic coded JPEG file at all.
-block N Set DCT block size. All N from 1 to 16 are possible.
Default is 8 (baseline format).
@@ -188,6 +188,25 @@ Switches for advanced users: so many decoders will be unable to view a reversible
color transformed JPEG file at all.
+ -bgycc Create big gamut YCC JPEG file.
+ In this type of encoding the color difference
+ components are quantized further by a factor of 2
+ compared to the normal Cb/Cr values, thus creating
+ space to allow larger color values with higher
+ saturation than the normal gamut limits to be encoded.
+ In order to compensate for the loss of color fidelity
+ compared to a normal YCC encoded file, the color
+ quantization tables can be adjusted accordingly.
+ For example, cjpeg -bgycc -quality 80,90 will give
+ similar results as cjpeg -quality 80.
+ CAUTION: For correct decompression a decoder with big
+ gamut YCC support (JFIF version 2) is required.
+ An old decoder may or may not display a big gamut YCC
+ encoded JPEG file, depending on JFIF version check
+ and corresponding warning/error configuration.
+ In case of a granted decompression the old decoder
+ will display the image with half saturated colors.
+
-dct int Use integer DCT method (default).
-dct fast Use fast integer DCT (less accurate).
-dct float Use floating-point DCT method.
@@ -387,7 +406,8 @@ quality settings to make very small JPEG files; the percentage improvement is often a lot more than it is on larger files. (At present, -optimize
mode is always selected when generating progressive JPEG files.)
-GIF input files are no longer supported, to avoid the Unisys LZW patent.
+GIF input files are no longer supported, to avoid the Unisys LZW patent
+(now expired).
(Conversion of GIF files to JPEG is usually a bad idea anyway.)
@@ -415,8 +435,9 @@ it may run out of memory even with -maxmemory 0. In that case you can still decompress, with some loss of image quality, by specifying -onepass for
one-pass quantization.
-To avoid the Unisys LZW patent, djpeg produces uncompressed GIF files. These
-are larger than they should be, but are readable by standard GIF decoders.
+To avoid the Unisys LZW patent (now expired), djpeg produces uncompressed GIF
+files. These are larger than they should be, but are readable by standard GIF
+decoders.
HINTS FOR BOTH PROGRAMS
@@ -533,14 +554,20 @@ image region but losslessly preserves what is inside. Like the rotate and flip transforms, lossless crop is restricted by the current JPEG format: the
upper left corner of the selected region must fall on an iMCU boundary. If
this does not hold for the given crop parameters, we silently move the upper
-left corner up and/or left to make it so, simultaneously increasing the region
-dimensions to keep the lower right crop corner unchanged. (Thus, the output
-image covers at least the requested region, but may cover more.)
+left corner up and/or left to make it so, simultaneously increasing the
+region dimensions to keep the lower right crop corner unchanged. (Thus, the
+output image covers at least the requested region, but may cover more.)
+The adjustment of the region dimensions may be optionally disabled.
The image can be losslessly cropped by giving the switch:
-crop WxH+X+Y Crop to a rectangular subarea of width W, height H
starting at point X,Y.
+A complementary lossless-wipe option is provided to discard (gray out) data
+inside a given image region while losslessly preserving what is outside:
+ -wipe WxH+X+Y Wipe (gray out) a rectangular subarea of
+ width W, height H starting at point X,Y.
+
Other not-strictly-lossless transformation switches are:
-grayscale Force grayscale output.
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