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Disable costly TraceBackwards for method=0.

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Disable costly TraceBackwards heuristic for computing the backward references
for low_effort (method=0) compression.

The TraceBackwards heuristic is already disabled for lower (q < 25) quality
range. Following is the compression data for 1000 image corpus for q >= 25.

This speeds up compression (q >= 25) by a factor of 2.5-3X with slight loss of
compression density (0.7% for lower quality range and 1.2% for higher qualities).

Change-Id: I256c9e2137c7de4083f423ea32ee12d3b0f46253
This commit is contained in:
Vikas Arora 2015-01-15 09:00:47 -08:00
parent a7e7caa486
commit b9e356b998
1 changed files with 3 additions and 2 deletions
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5
src/enc/backward_references.c
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@ -1017,8 +1017,9 @@ VP8LBackwardRefs* VP8LGetBackwardReferences(
// Choose appropriate backward reference.
if (lz77_is_useful) {
// TraceBackwards is costly. Don't execute it at lower quality.
const int try_lz77_trace_backwards = (quality >= 25);
// TraceBackwards is costly. Don't execute it at lower quality or low effort
// compression setting.
const int try_lz77_trace_backwards = (quality >= 25) && !low_effort;
best = refs_lz77; // default guess: lz77 is better
if (try_lz77_trace_backwards) {
VP8LBackwardRefs* const refs_trace = refs_rle;