enc_gaborish.cc - mozsearch

// 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/enc_gaborish.h"

#include <jxl/memory_manager.h>

#include <hwy/base.h>

#include "lib/jxl/base/data_parallel.h"

#include "lib/jxl/base/rect.h"

#include "lib/jxl/base/status.h"

#include "lib/jxl/convolve.h"

#include "lib/jxl/image.h"

#include "lib/jxl/image_ops.h"

namespace jxl {

Status GaborishInverse(Image3F* in_out, const Rect& rect, const float mul[3],

                       ThreadPool* pool) {

  JxlMemoryManager* memory_manager = in_out->memory_manager();

  WeightsSymmetric5 weights[3];

  // Only an approximation. One or even two 3x3, and rank-1 (separable) 5x5

  // are insufficient. The numbers here have been obtained by butteraugli

  // based optimizing the whole system and the errors produced are likely

  // more favorable for good rate-distortion compromises rather than

  // just using mathematical optimization to find the inverse.

  static const float kGaborish[5] = {

      -0.09495815671340026, -0.041031725066768575,  0.013710004822696948,

      0.006510206083837737, -0.0014789063378272242,

};

  for (int i = 0; i < 3; ++i) {

    double sum = 1.0 + mul[i] * 4 *

                           (kGaborish[0] + kGaborish[1] + kGaborish[2] +

                            kGaborish[4] + 2 * kGaborish[3]);

    if (sum < 1e-5) {

      sum = 1e-5;

    const float normalize = static_cast<float>(1.0 / sum);

    const float normalize_mul = mul[i] * normalize;

    weights[i] = WeightsSymmetric5{{HWY_REP4(normalize)},

                                   {HWY_REP4(normalize_mul * kGaborish[0])},

                                   {HWY_REP4(normalize_mul * kGaborish[2])},

                                   {HWY_REP4(normalize_mul * kGaborish[1])},

                                   {HWY_REP4(normalize_mul * kGaborish[4])},

                                   {HWY_REP4(normalize_mul * kGaborish[3])}};

  // Reduce memory footprint by only allocating a single plane and swapping it

  // into the output Image3F. Better still would be tiling.

  // Note that we cannot *allocate* a plane, as doing so might cause Image3F to

  // have planes of different stride. Instead, we copy one plane in a temporary

  // image and reuse the existing planes of the in/out image.

  ImageF temp;

  JXL_ASSIGN_OR_RETURN(temp,

                       ImageF::Create(memory_manager, in_out->Plane(2).xsize(),

                                      in_out->Plane(2).ysize()));

  JXL_RETURN_IF_ERROR(CopyImageTo(in_out->Plane(2), &temp));

  Rect xrect = rect.Extend(3, Rect(*in_out));

  JXL_RETURN_IF_ERROR(Symmetric5(in_out->Plane(0), xrect, weights[0], pool,

                                 &in_out->Plane(2), xrect));

  JXL_RETURN_IF_ERROR(Symmetric5(in_out->Plane(1), xrect, weights[1], pool,

                                 &in_out->Plane(0), xrect));

  JXL_RETURN_IF_ERROR(

      Symmetric5(temp, xrect, weights[2], pool, &in_out->Plane(1), xrect));

  // Now planes are 1, 2, 0.

  in_out->Plane(0).Swap(in_out->Plane(1));

  // 2 1 0

  in_out->Plane(0).Swap(in_out->Plane(2));

  return true;

}  // namespace jxl