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lossless: make prediction in encoder work per scanline

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instead of per block. This prepares for a next CL that can make the
predictors alter RGB value behind transparent pixels for denser
encoding. Some predictors depend on the top-right pixel, and it must
have been already processed to know its new RGB value, so requires per
scanline instead of per block.

Running the encode speed test on 1000 PNGs 10 times with default
settings:
Before:
Compression (output/input): 2.3745/3.2667 bpp, Encode rate (raw data): 1.497 MP/s
After:
Compression (output/input): 2.3745/3.2667 bpp, Encode rate (raw data): 1.501 MP/s

Same but with quality 0, method 0 and 30 iterations:
Before:
Compression (output/input): 2.9120/3.2667 bpp, Encode rate (raw data): 36.379 MP/s
After:
Compression (output/input): 2.9120/3.2667 bpp, Encode rate (raw data): 36.462 MP/s

No effect on compressed size, this produces exactly same files. No
significant measured effect on speed. Expected faster speed from better
memory layout with scanline processing but slower speed due to needing
to get predictor mode per pixel, may compensate each other.

Change-Id: I40f766f1c1c19f87b62c1e2a1c4cd7627a2c3334
This commit is contained in:
Lode Vandevenne
2015-11-24 13:50:18 +00:00
committed by Pascal Massimino
parent 5cd2ef4c4a
commit 239421c5ef
2 changed files with 62 additions and 57 deletions
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4
src/enc/vp8l.c
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@ -1123,8 +1123,10 @@ static WebPEncodingError AllocateTransformBuffer(VP8LEncoder* const enc,
if (enc->argb_ == NULL) {
const int tile_size = 1 << enc->transform_bits_;
const uint64_t image_size = width * height;
// Ensure enough size for tiles, as well as for two scanlines and two
// extra pixels for CopyImageWithPrediction.
const uint64_t argb_scratch_size =
enc->use_predict_ ? tile_size * width + width : 0;
enc->use_predict_ ? tile_size * width + width + 2 : 0;
const int transform_data_size =
(enc->use_predict_ || enc->use_cross_color_)
? VP8LSubSampleSize(width, enc->transform_bits_) *