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The fast integer DCT degrades for qualities > 95, so use the slow integer DCT instead to ensure that perceptually lossless performance is maintained.

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DRC
2011-01-25 06:52:31 +00:00
parent 9ca11b80fc
commit 21b5c4bc4d
2 changed files with 12 additions and 1 deletions
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10
ChangeLog.txt
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@@ -1,3 +1,13 @@
Significant changes since 1.0.90
================================
[1] Since the fast integer forward DCT seems to degrade for JPEG qualities
greater than 95, TurboJPEG/OSS will now automatically use the slow integer
forward DCT when generating JPEG images of quality 96 or greater. This
reduces compression performance by as much as 15% for these high-quality images
but is necessary to ensure that the images are perceptually lossless.
Significant changes since 1.0.1
===============================

3
turbojpegl.c
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@@ -193,7 +193,8 @@ DLLEXPORT int DLLCALL tjCompress(tjhandle h,
jpeg_set_colorspace(&j->cinfo, JCS_GRAYSCALE);
else
jpeg_set_colorspace(&j->cinfo, JCS_YCbCr);
j->cinfo.dct_method = JDCT_FASTEST;
if(qual>=96) j->cinfo.dct_method=JDCT_ISLOW;
else j->cinfo.dct_method=JDCT_FASTEST;
j->cinfo.comp_info[0].h_samp_factor=hsampfactor[jpegsub];
j->cinfo.comp_info[1].h_samp_factor=1;