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Disable extended baseline mode in clustering by default. #106

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Feb 11, 2025
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Disable extended baseline mode in clustering by default. #106

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12 changes: 11 additions & 1 deletion lib/jpegli/entropy_coding.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <limits>
#include <vector>

#include "lib/base/bits.h"
Expand Down Expand Up @@ -585,13 +586,22 @@ void ClusterJpegHistograms(j_compress_ptr cinfo, const Histogram* histograms,
clusters->histogram_indexes.resize(num);
std::vector<uint32_t> slot_histograms;
std::vector<float> slot_costs;
// Since not all jpeg decoders support the extended sequential mode, i.e. the
// 0xff 0xc1 SOF marker, we will limit the number of clusters to 2 in
// sequential mode, unless the quantization tables already require the
// extended sequential mode.
const bool force_baseline =
!cinfo->progressive_mode && cinfo->master->force_baseline;

for (size_t i = 0; i < num; ++i) {
const Histogram& cur = histograms[i];
if (IsEmptyHistogram(cur)) {
continue;
}
float best_cost = HistogramCost(cur);
size_t best_slot = slot_histograms.size();
float best_cost = force_baseline && best_slot > 1
? std::numeric_limits<float>::max()
: HistogramCost(cur);
for (size_t j = 0; j < slot_histograms.size(); ++j) {
size_t prev_idx = slot_histograms[j];
const Histogram& prev = clusters->histograms[prev_idx];
Expand Down
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