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WebP/Lossy: Add a missing clamp() in TM_PRED prediction

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The spec has that clamp at the end of
https://datatracker.ietf.org/doc/html/rfc6386#section-12.2:

    The exact algorithm is as follows:
    [...]
               b[r][c] = clamp255(L[r]+ A[c] - P);

For the test images I'm looking at, it doesn't seem to make a
dramatic difference, but omitting it in `B_TM_PRED` did make
a dramatic difference, so add it. (Also, the spec demands it.)
This commit is contained in:
Nico Weber 2023-05-31 09:08:26 -04:00 • committed by Andreas Kling
parent 40e1ec6cf9
commit 830a3a25dc
Notes: sideshowbarker 2024-07-17 00:37:23 +09:00
1 changed files with 1 additions and 1 deletions
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Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp
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@ -924,7 +924,7 @@ void predict_macroblock(Span<i16> prediction, IntraMacroblockMode mode, int mb_x
VERIFY(mode == TM_PRED);
for (int y = 0; y < N; ++y)
for (int x = 0; x < N; ++x)
prediction[y * N + x] = left[y] + above[mb_x * N + x] - truemotion_corner;
prediction[y * N + x] = clamp(left[y] + above[mb_x * N + x] - truemotion_corner, 0, 255);
}
}