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Tune Lossless compression for lower qualities.

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This is required for WebP lossy+Alpha images, where Alpha channel is taking
60-70% of the compression (CPU) cycles.

Also evaluated on 1000 PNG corpus and overall compression speed
is 15-40% better for lossy (PNG+Alpha) compression.
The pure lossless compression numbers are almost same (or little
better) with this change.

Change-Id: I9e5ae7372ed6227a9a5b64cd9cff84c747195a57
This commit is contained in:
Vikas Arora
2013-03-05 22:05:00 +00:00
committed by James Zern
parent 19eb012c55
commit 0478b5d214
3 changed files with 6 additions and 11 deletions
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2
src/enc/alpha.c
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@ -80,7 +80,7 @@ static int EncodeLossless(const uint8_t* const data, int width, int height,
config.lossless = 1;
config.method = effort_level; // impact is very small
// Set a moderate default quality setting for alpha.
config.quality = 6.f * effort_level;
config.quality = 5.f * effort_level;
assert(config.quality >= 0 && config.quality <= 100.f);
ok = VP8LBitWriterInit(&tmp_bw, (width * height) >> 3);