Fix bug in remap #2028
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Fix bug in remap #2028
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Pull request overview
This PR fixes a bug in the remapInter function where RGB values were being zeroed when the alpha channel was zero. The fix removes alpha-based weight adjustment during pixel interpolation, preserving RGB values while still allowing alpha masking.
Key Changes:
- Removed the conditional alpha weight multiplication for RGBAfColor pixels during area interpolation
- This ensures RGB values are preserved in the weighted average regardless of alpha values
- Alpha channel itself will still be averaged, correctly indicating masking when all source pixels have alpha=0
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| const P & pix = source(by, bx); | ||
| double weight = yocc * xocc; | ||
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| if constexpr (std::is_same<P, RGBAfColor>()) | ||
| { | ||
| weight *= pix.a(); | ||
| } | ||
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| sum += pix * weight; | ||
| wsum += weight; |
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This bug fix lacks test coverage. The image module has comprehensive test files (image_test.cpp, filtering_test.cpp, resampling_test.cpp), but there are no tests for the remap functionality. Consider adding a test case that verifies:
- RGB values are preserved when alpha=0 (the bug being fixed)
- The weighted averaging still works correctly for downsampling
- Alpha channel handling is correct for various input scenarios
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CedricThebault
approved these changes
Dec 2, 2025
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Remap was zeroing rgb values when alpha was zero. We want to keep the masked values but only mask it with alpha = 0.