LibGfx/WebPWriter: Do not write color index if only one channel varies #24503
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The benefit of the color indexing transform is to have only one varying channel after it (the green channel, which after the transform serves as index into the color table). If there is only one varying channel before the transform, it's not beneficial. (...except if there are <= 16 colors, then the pixel bundling presumably still works.)
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AtkinsSJ
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The color indexing transform shouldn't make single-channel images larger (by needlessly writing a palette). If there <= 16 colors in the single channel, it should make the image smaller.
timschumi
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Jun 1, 2024
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The benefit of the color indexing transform is to have only one
varying channel after it (the green channel, which after the
transform serves as index into the color table).
If there is only one varying channel before the transform, it's
not beneficial. (...except if there are <= 16 colors, then the
pixel bundling presumably still works.)
Small FIXME-fix after #24483.