LibGfx: Make Bayer dithering more luminosity-conservative #26433
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Huh this seems to share a fix with #26432 |
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Yeah, I'm writing a comment to explain it and I wanted to open that first to be able to reference it. But now I'm wondering if it's actually the best approach. |
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On average, this patch reduces the error in luminosity between an input image and its dithered equivalent. This is done by correcting an off-by- one error in the threshold computation and also by making sure the range of mapped gray values to matrix pattern is of equal size for all ranges. This means that all values between 0 and 255 / (N * N + 1) (51 for Bayer2x2) will result in a black pixel while only a value of 0 would previously do it. The test works by first generating gray bitmap, then applying Bayer dithering on them and finally compare the luminosity of the two.
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On average, this patch reduces the error in luminosity between an input image and its dithered equivalent. This is done by correcting an off-by-one error in the threshold computation and also by making sure the range of mapped gray values to matrix pattern is of equal size for all ranges. This means that all values between 0 and 255 / (N * N + 1) (51 for
Bayer2x2) will result in a black pixel while only a value of 0 would previously do it.
The test works by first generating gray bitmap, then applying Bayer dithering on them and finally compare the luminosity of the two.
For a Bayer2x2:
After fixing off-by-one:
After the full patch: