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Merge pull request #28667 from jules-ai:jules_fix_jpeg_sampling_factor

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Fix JPEG chroma configuration & Standardize component settings #28667

### Problem

Incorrectly treated Chroma as a single channel. In $YC_bC_r$, chroma must be set in both separate channels ($C_b$ and $C_r$).

### Fix
- Explicit Setup: Configured all three components ($Y$, $C_b$, $C_r$) individually.
- Standardization: Removed reliance on library defaults to prevent undefined behavior.


### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [ ] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake
This commit is contained in:
Jules
2026-05-24 16:41:17 +08:00
committed by GitHub
parent dd214962a5
commit ffd0cf49a7
1 changed files with 7 additions and 3 deletions
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modules/imgcodecs/src/grfmt_jpeg.cpp
+7 -3
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@@ -825,10 +825,12 @@ bool JpegEncoder::write( const Mat& img, const std::vector<int>& params )
if( (channels > 1) && ( sampling_factor != 0 ) )
{
cinfo.comp_info[0].v_samp_factor = (sampling_factor >> 16 ) & 0xF;
cinfo.comp_info[0].h_samp_factor = (sampling_factor >> 20 ) & 0xF;
cinfo.comp_info[1].v_samp_factor = 1;
cinfo.comp_info[1].h_samp_factor = 1;
cinfo.comp_info[0].v_samp_factor = (sampling_factor >> 16 ) & 0xF;
cinfo.comp_info[1].h_samp_factor = (sampling_factor >> 12 ) & 0xF;
cinfo.comp_info[1].v_samp_factor = (sampling_factor >> 8 ) & 0xF;
cinfo.comp_info[2].h_samp_factor = (sampling_factor >> 4 ) & 0xF;
cinfo.comp_info[2].v_samp_factor = (sampling_factor >> 0 ) & 0xF;
}
if (luma_quality >= 0 && chroma_quality >= 0)
@@ -843,6 +845,8 @@ bool JpegEncoder::write( const Mat& img, const std::vector<int>& params )
cinfo.comp_info[0].h_samp_factor = 1;
cinfo.comp_info[1].v_samp_factor = 1;
cinfo.comp_info[1].h_samp_factor = 1;
cinfo.comp_info[2].v_samp_factor = 1;
cinfo.comp_info[2].h_samp_factor = 1;
}
jpeg_default_qtables( &cinfo, TRUE );
#else