tor-browser

quantizer.cc (5682B)

---

// Copyright (c) the JPEG XL Project Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#include "lib/jxl/quantizer.h"

#include <algorithm>
#include <cstring>

#include "lib/jxl/base/compiler_specific.h"
#include "lib/jxl/base/rect.h"
#include "lib/jxl/field_encodings.h"
#include "lib/jxl/fields.h"
#include "lib/jxl/image.h"
#include "lib/jxl/image_ops.h"
#include "lib/jxl/quant_weights.h"

namespace jxl {

static const int32_t kDefaultQuant = 64;

#if JXL_CXX_LANG < JXL_CXX_17
constexpr int32_t Quantizer::kQuantMax;
#endif

Quantizer::Quantizer(const DequantMatrices& dequant)
   : Quantizer(dequant, kDefaultQuant, kGlobalScaleDenom / kDefaultQuant) {}

Quantizer::Quantizer(const DequantMatrices& dequant, int quant_dc,
                    int global_scale)
   : global_scale_(global_scale), quant_dc_(quant_dc), dequant_(&dequant) {
 RecomputeFromGlobalScale();
 inv_quant_dc_ = inv_global_scale_ / quant_dc_;

 memcpy(zero_bias_, kZeroBiasDefault, sizeof(kZeroBiasDefault));
}

void Quantizer::ComputeGlobalScaleAndQuant(float quant_dc, float quant_median,
                                          float quant_median_absd) {
 // Target value for the median value in the quant field.
 const float kQuantFieldTarget = 5;
 // We reduce the median of the quant field by the median absolute deviation:
 // higher resolution on highly varying quant fields.
 float scale = kGlobalScaleDenom * (quant_median - quant_median_absd) /
               kQuantFieldTarget;
 // Ensure that new_global_scale is positive and no more than 1<<15.
 if (scale < 1) scale = 1;
 if (scale > (1 << 15)) scale = 1 << 15;
 int new_global_scale = static_cast<int>(scale);
 // Ensure that quant_dc_ will always be at least
 // 0.625 * kGlobalScaleDenom/kGlobalScaleNumerator = 10.
 const int scaled_quant_dc =
     static_cast<int>(quant_dc * kGlobalScaleNumerator * 1.6);
 if (new_global_scale > scaled_quant_dc) {
   new_global_scale = scaled_quant_dc;
   if (new_global_scale <= 0) new_global_scale = 1;
 }
 global_scale_ = new_global_scale;
 // Code below uses inv_global_scale_.
 RecomputeFromGlobalScale();

 float fval = quant_dc * inv_global_scale_ + 0.5f;
 fval = std::min<float>(1 << 16, fval);
 const int new_quant_dc = static_cast<int>(fval);
 quant_dc_ = new_quant_dc;

 // quant_dc_ was updated, recompute values.
 RecomputeFromGlobalScale();
}

void Quantizer::SetQuantFieldRect(const ImageF& qf, const Rect& rect,
                                 ImageI* JXL_RESTRICT raw_quant_field) const {
 for (size_t y = 0; y < rect.ysize(); ++y) {
   const float* JXL_RESTRICT row_qf = rect.ConstRow(qf, y);
   int32_t* JXL_RESTRICT row_qi = rect.Row(raw_quant_field, y);
   for (size_t x = 0; x < rect.xsize(); ++x) {
     int val = ClampVal(row_qf[x] * inv_global_scale_ + 0.5f);
     row_qi[x] = val;
   }
 }
}

Status Quantizer::SetQuantField(const float quant_dc, const ImageF& qf,
                               ImageI* JXL_RESTRICT raw_quant_field) {
 std::vector<float> data(qf.xsize() * qf.ysize());
 for (size_t y = 0; y < qf.ysize(); ++y) {
   const float* JXL_RESTRICT row_qf = qf.Row(y);
   for (size_t x = 0; x < qf.xsize(); ++x) {
     float quant = row_qf[x];
     data[qf.xsize() * y + x] = quant;
   }
 }
 std::nth_element(data.begin(), data.begin() + data.size() / 2, data.end());
 const float quant_median = data[data.size() / 2];
 std::vector<float> deviations(data.size());
 for (size_t i = 0; i < data.size(); i++) {
   deviations[i] = fabsf(data[i] - quant_median);
 }
 std::nth_element(deviations.begin(),
                  deviations.begin() + deviations.size() / 2,
                  deviations.end());
 const float quant_median_absd = deviations[deviations.size() / 2];
 ComputeGlobalScaleAndQuant(quant_dc, quant_median, quant_median_absd);
 if (raw_quant_field) {
   JXL_ENSURE(SameSize(*raw_quant_field, qf));
   SetQuantFieldRect(qf, Rect(qf), raw_quant_field);
 }
 return true;
}

void Quantizer::SetQuant(float quant_dc, float quant_ac,
                        ImageI* JXL_RESTRICT raw_quant_field) {
 ComputeGlobalScaleAndQuant(quant_dc, quant_ac, 0);
 int32_t val = ClampVal(quant_ac * inv_global_scale_ + 0.5f);
 FillImage(val, raw_quant_field);
}

Status QuantizerParams::VisitFields(Visitor* JXL_RESTRICT visitor) {
 JXL_QUIET_RETURN_IF_ERROR(visitor->U32(
     BitsOffset(11, 1), BitsOffset(11, 2049), BitsOffset(12, 4097),
     BitsOffset(16, 8193), 1, &global_scale));
 JXL_QUIET_RETURN_IF_ERROR(visitor->U32(Val(16), BitsOffset(5, 1),
                                        BitsOffset(8, 1), BitsOffset(16, 1), 1,
                                        &quant_dc));
 return true;
}

QuantizerParams Quantizer::GetParams() const {
 QuantizerParams params;
 params.global_scale = global_scale_;
 params.quant_dc = quant_dc_;
 return params;
}

Status Quantizer::Decode(BitReader* reader) {
 QuantizerParams params;
 JXL_RETURN_IF_ERROR(Bundle::Read(reader, &params));
 global_scale_ = static_cast<int>(params.global_scale);
 quant_dc_ = static_cast<int>(params.quant_dc);
 RecomputeFromGlobalScale();
 return true;
}

void Quantizer::DumpQuantizationMap(const ImageI& raw_quant_field) const {
 printf("Global scale: %d (%.7f)\nDC quant: %d\n", global_scale_,
        global_scale_ * 1.0 / kGlobalScaleDenom, quant_dc_);
 printf("AC quantization Map:\n");
 for (size_t y = 0; y < raw_quant_field.ysize(); ++y) {
   for (size_t x = 0; x < raw_quant_field.xsize(); ++x) {
     printf(" %3d", raw_quant_field.Row(y)[x]);
   }
   printf("\n");
 }
}

}  // namespace jxl