1 // Copyright (c) the JPEG XL Project Authors. All rights reserved.
3 // Use of this source code is governed by a BSD-style
4 // license that can be found in the LICENSE file.
6 // Library to encode the context map.
8 #include "lib/jxl/enc_context_map.h"
16 #include "lib/jxl/base/bits.h"
17 #include "lib/jxl/base/status.h"
18 #include "lib/jxl/enc_ans.h"
19 #include "lib/jxl/enc_aux_out.h"
20 #include "lib/jxl/entropy_coder.h"
21 #include "lib/jxl/pack_signed.h"
27 size_t IndexOf(const std::vector<uint8_t>& v, uint8_t value) {
29 for (; i < v.size(); ++i) {
30 if (v[i] == value) return i;
35 void MoveToFront(std::vector<uint8_t>* v, size_t index) {
36 uint8_t value = (*v)[index];
37 for (size_t i = index; i != 0; --i) {
38 (*v)[i] = (*v)[i - 1];
43 std::vector<uint8_t> MoveToFrontTransform(const std::vector<uint8_t>& v) {
44 if (v.empty()) return v;
45 uint8_t max_value = *std::max_element(v.begin(), v.end());
46 std::vector<uint8_t> mtf(max_value + 1);
47 for (size_t i = 0; i <= max_value; ++i) mtf[i] = i;
48 std::vector<uint8_t> result(v.size());
49 for (size_t i = 0; i < v.size(); ++i) {
50 size_t index = IndexOf(mtf, v[i]);
51 JXL_ASSERT(index < mtf.size());
52 result[i] = static_cast<uint8_t>(index);
53 MoveToFront(&mtf, index);
60 void EncodeContextMap(const std::vector<uint8_t>& context_map,
61 size_t num_histograms, BitWriter* writer, size_t layer,
63 if (num_histograms == 1) {
71 std::vector<uint8_t> transformed_symbols = MoveToFrontTransform(context_map);
72 std::vector<std::vector<Token>> tokens(1), mtf_tokens(1);
73 EntropyEncodingData codes;
74 std::vector<uint8_t> sink_context_map;
75 for (size_t i = 0; i < context_map.size(); i++) {
76 tokens[0].emplace_back(0, context_map[i]);
78 for (size_t i = 0; i < transformed_symbols.size(); i++) {
79 mtf_tokens[0].emplace_back(0, transformed_symbols[i]);
81 HistogramParams params;
82 params.uint_method = HistogramParams::HybridUintMethod::kContextMap;
83 size_t ans_cost = BuildAndEncodeHistograms(
84 params, 1, tokens, &codes, &sink_context_map, nullptr, 0, nullptr);
85 size_t mtf_cost = BuildAndEncodeHistograms(
86 params, 1, mtf_tokens, &codes, &sink_context_map, nullptr, 0, nullptr);
87 bool use_mtf = mtf_cost < ans_cost;
88 // Rebuild token list.
90 for (size_t i = 0; i < transformed_symbols.size(); i++) {
91 tokens[0].emplace_back(0,
92 use_mtf ? transformed_symbols[i] : context_map[i]);
94 size_t entry_bits = CeilLog2Nonzero(num_histograms);
95 size_t simple_cost = entry_bits * context_map.size();
96 if (entry_bits < 4 && simple_cost < ans_cost && simple_cost < mtf_cost) {
98 writer->Write(2, entry_bits);
99 for (size_t i = 0; i < context_map.size(); i++) {
100 writer->Write(entry_bits, context_map[i]);
104 writer->Write(1, use_mtf); // Use/don't use MTF.
105 BuildAndEncodeHistograms(params, 1, tokens, &codes, &sink_context_map,
106 writer, layer, aux_out);
107 WriteTokens(tokens[0], codes, sink_context_map, writer);
111 void EncodeBlockCtxMap(const BlockCtxMap& block_ctx_map, BitWriter* writer,
113 auto& dct = block_ctx_map.dc_thresholds;
114 auto& qft = block_ctx_map.qf_thresholds;
115 auto& ctx_map = block_ctx_map.ctx_map;
116 BitWriter::Allotment allotment(
118 (dct[0].size() + dct[1].size() + dct[2].size() + qft.size()) * 34 + 1 +
119 4 + 4 + ctx_map.size() * 10 + 1024);
120 if (dct[0].empty() && dct[1].empty() && dct[2].empty() && qft.empty() &&
121 ctx_map.size() == 21 &&
122 std::equal(ctx_map.begin(), ctx_map.end(), BlockCtxMap::kDefaultCtxMap)) {
123 writer->Write(1, 1); // default
124 allotment.ReclaimAndCharge(writer, kLayerAC, aux_out);
128 for (int j : {0, 1, 2}) {
129 writer->Write(4, dct[j].size());
130 for (int i : dct[j]) {
131 JXL_CHECK(U32Coder::Write(kDCThresholdDist, PackSigned(i), writer));
134 writer->Write(4, qft.size());
135 for (uint32_t i : qft) {
136 JXL_CHECK(U32Coder::Write(kQFThresholdDist, i - 1, writer));
138 EncodeContextMap(ctx_map, block_ctx_map.num_ctxs, writer, kLayerAC, aux_out);
139 allotment.ReclaimAndCharge(writer, kLayerAC, aux_out);