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Fix pair update in stochastic entropy merging.

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The old code simply did not make sense.
The effect is that the pair would be popped from the
queue no matter what; as the queue is small, it does
not matter that much on the results.
But it will matter for a later CL.

Change-Id: If50c9fa9d7f3ac3c48bb7336d81479287d4944c4
This commit is contained in:
Vincent Rabaud 2018-11-07 00:33:14 +01:00
parent 4cd0582d50
commit 485ff86fbb
1 changed files with 15 additions and 7 deletions
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22
src/enc/histogram_enc.c
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@ -756,6 +756,18 @@ static void HistoQueueUpdateHead(HistoQueue* const histo_queue,
}
}
// Update the cost diff and combo of a pair of histograms. This needs to be
// called when the the histograms have been merged with a third one.
static void HistoQueueUpdatePair(const VP8LHistogram* const h1,
const VP8LHistogram* const h2,
double threshold,
HistogramPair* const pair) {
const double sum_cost = h1->bit_cost_ + h2->bit_cost_;
pair->cost_combo = 0.;
GetCombinedHistogramEntropy(h1, h2, sum_cost + threshold, &pair->cost_combo);
pair->cost_diff = pair->cost_combo - sum_cost;
}
// Create a pair from indices "idx1" and "idx2" provided its cost
// is inferior to "threshold", a negative entropy.
// It returns the cost of the pair, or 0. if it superior to threshold.
@ -765,7 +777,6 @@ static double HistoQueuePush(HistoQueue* const histo_queue,
const VP8LHistogram* h1;
const VP8LHistogram* h2;
HistogramPair pair;
double sum_cost;
assert(threshold <= 0.);
if (idx1 > idx2) {
@ -777,10 +788,8 @@ static double HistoQueuePush(HistoQueue* const histo_queue,
pair.idx2 = idx2;
h1 = histograms[idx1];
h2 = histograms[idx2];
sum_cost = h1->bit_cost_ + h2->bit_cost_;
pair.cost_combo = 0.;
GetCombinedHistogramEntropy(h1, h2, sum_cost + threshold, &pair.cost_combo);
pair.cost_diff = pair.cost_combo - sum_cost;
HistoQueueUpdatePair(h1, h2, threshold, &pair);
// Do not even consider the pair if it does not improve the entropy.
if (pair.cost_diff >= threshold) return 0.;
@ -973,8 +982,7 @@ static int HistogramCombineStochastic(VP8LHistogramSet* const image_histo,
}
if (do_eval) {
// Re-evaluate the cost of an updated pair.
GetCombinedHistogramEntropy(histograms[p->idx1], histograms[p->idx2], 0,
&p->cost_diff);
HistoQueueUpdatePair(histograms[p->idx1], histograms[p->idx2], 0., p);
if (p->cost_diff >= 0.) {
HistoQueuePopPair(&histo_queue, p);
continue;