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gif2webp: Improved compression for lossy animated WebP

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We reduce transparency by turning some transparent pixels into
corresponding RGB values from previous canvas.

This improves compression by about 23%.

Change-Id: I02d70a43a1d0906ac09a7e2dc510be3b2d38f593
This commit is contained in:
Urvang Joshi
2013-09-30 16:48:39 -07:00
parent fb887f7fe6
commit 606c4304c4
3 changed files with 29 additions and 0 deletions
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5
examples/gif2webp.c
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@ -166,6 +166,11 @@ static int OptimizeAndEncodeFrame(
// Update prev_canvas by simply copying from 'curr'.
WebPUtilCopyPixels(curr, prev_canvas);
} else {
if (!config->lossless) {
// For lossy compression, it's better to replace transparent pixels of
// 'curr' with actual RGB values, whenever possible.
WebPUtilReduceTransparency(prev_canvas, &rect, curr);
}
if (!WebPFrameCacheShouldTryKeyFrame(cache)) {
// Add this as a frame rectangle.
if (!WebPFrameCacheAddFrame(cache, config, info, sub_image, NULL, NULL)) {