diff options
author | Eirik Aavitsland <eirik.aavitsland@qt.io> | 2018-04-04 09:17:16 +0200 |
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committer | Eirik Aavitsland <eirik.aavitsland@qt.io> | 2018-04-06 06:40:37 +0000 |
commit | cab5f37ef48d996529416913d912e8e8a2b061f5 (patch) | |
tree | 58e46da53097015053a3eee5ccfe6bf5262c119d | |
parent | 0ee5cbb1a449e05270454dfb6151438b04a5cb84 (diff) |
Fix visual artifacts in diffuse image dithering (the default)
The distributed error fractions in the Floyd-Steinberg dithering
algorithm were not computed precisely. In particular, rounding errors
could be accumulated, leading to visual artifacts.
Task-number: QTBUG-67425
Change-Id: I77b48c3cab3e66ca161721d14b58fcc4188e74a8
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
-rw-r--r-- | src/gui/image/qimage_conversions.cpp | 12 |
1 files changed, 8 insertions, 4 deletions
diff --git a/src/gui/image/qimage_conversions.cpp b/src/gui/image/qimage_conversions.cpp index 4eef617336..1b4d3e63dd 100644 --- a/src/gui/image/qimage_conversions.cpp +++ b/src/gui/image/qimage_conversions.cpp @@ -1333,14 +1333,18 @@ void dither_to_Mono(QImageData *dst, const QImageData *src, } else { bit--; } + const int e7 = ((err * 7) + 8) >> 4; + const int e5 = ((err * 5) + 8) >> 4; + const int e3 = ((err * 3) + 8) >> 4; + const int e1 = err - (e7 + e5 + e3); if (x < w) - *b1 += (err*7)>>4; // spread error to right pixel + *b1 += e7; // spread error to right pixel if (not_last_line) { - b2[0] += (err*5)>>4; // pixel below + b2[0] += e5; // pixel below if (x > 1) - b2[-1] += (err*3)>>4; // pixel below left + b2[-1] += e3; // pixel below left if (x < w) - b2[1] += err>>4; // pixel below right + b2[1] += e1; // pixel below right } b2++; } |