From a4183d94c77eed4adfbfdb959e3c7fe9ea8009f1 Mon Sep 17 00:00:00 2001 From: Vincent Rabaud Date: Fri, 28 Mar 2025 15:00:41 +0100 Subject: [PATCH] Remove the computation of ExtraCost when comparing histograms Entropy clustering merges symbol histograms to reduce the overall entropy. The cost of 2 added histograms is compared to the 2 costs of the individual histograms and if it is smaller, a merge is done. Except for some symbols (distance and length), the computed cost is the real final cost based on the histogram, and some constant cost (independent from the probabilities of the symbols and hence the merge) because the symbol is encode as Golomb. This constant cost is useless and can be removed. Change-Id: I6271e8c0e4111cdeff544cbdb7dec3c67be5309c --- src/enc/histogram_enc.c | 22 ++++++++-------------- 1 file changed, 8 insertions(+), 14 deletions(-) diff --git a/src/enc/histogram_enc.c b/src/enc/histogram_enc.c index e210549b..ef43a1ef 100644 --- a/src/enc/histogram_enc.c +++ b/src/enc/histogram_enc.c @@ -401,10 +401,8 @@ WEBP_NODISCARD static int GetCombinedHistogramEntropy( *cost = GetCombinedEntropy(a->literal_, b->literal_, VP8LHistogramNumCodes(palette_code_bits), a->is_used_[0], b->is_used_[0], 0); - *cost += (uint64_t)VP8LExtraCostCombined(a->literal_ + NUM_LITERAL_CODES, - b->literal_ + NUM_LITERAL_CODES, - NUM_LENGTH_CODES) - << LOG_2_PRECISION_BITS; + // No need to add the extra cost as it is a constant that does not influence + // the histograms. if (*cost >= cost_threshold) return 0; if (a->trivial_symbol_ != VP8L_NON_TRIVIAL_SYM && @@ -434,9 +432,8 @@ WEBP_NODISCARD static int GetCombinedHistogramEntropy( *cost += GetCombinedEntropy(a->distance_, b->distance_, NUM_DISTANCE_CODES, a->is_used_[4], b->is_used_[4], 0); - *cost += (uint64_t)VP8LExtraCostCombined(a->distance_, b->distance_, - NUM_DISTANCE_CODES) - << LOG_2_PRECISION_BITS; + // No need to add the extra cost as it is a constant that does not influence + // the histograms. if (*cost >= cost_threshold) return 0; return 1; @@ -528,16 +525,13 @@ static void UpdateHistogramCost(VP8LHistogram* const h) { uint32_t alpha_sym, red_sym, blue_sym; const uint64_t alpha_cost = PopulationCost(h->alpha_, NUM_LITERAL_CODES, &alpha_sym, &h->is_used_[3]); + // No need to add the extra cost as it is a constant that does not influence + // the histograms. const uint64_t distance_cost = - PopulationCost(h->distance_, NUM_DISTANCE_CODES, NULL, &h->is_used_[4]) + - ((uint64_t)VP8LExtraCost(h->distance_, NUM_DISTANCE_CODES) - << LOG_2_PRECISION_BITS); + PopulationCost(h->distance_, NUM_DISTANCE_CODES, NULL, &h->is_used_[4]); const int num_codes = VP8LHistogramNumCodes(h->palette_code_bits_); h->literal_cost_ = - PopulationCost(h->literal_, num_codes, NULL, &h->is_used_[0]) + - ((uint64_t)VP8LExtraCost(h->literal_ + NUM_LITERAL_CODES, - NUM_LENGTH_CODES) - << LOG_2_PRECISION_BITS); + PopulationCost(h->literal_, num_codes, NULL, &h->is_used_[0]); h->red_cost_ = PopulationCost(h->red_, NUM_LITERAL_CODES, &red_sym, &h->is_used_[1]); h->blue_cost_ =