libjxl

quantizer.cc (5630B)

---

 // 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 <string.h>
 
 #include <algorithm>
 
 #include "lib/jxl/base/compiler_specific.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;
 
 constexpr int32_t Quantizer::kQuantMax;
 
 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) {
   JXL_ASSERT(dequant_ != nullptr);
   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;
     }
   }
 }
 
 void 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_CHECK(SameSize(*raw_quant_field, qf));
     SetQuantFieldRect(qf, Rect(qf), raw_quant_field);
   }
 }
 
 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