enc_comparator.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_comparator.h"

#include <jxl/memory_manager.h>

#include <algorithm>

#include <cstddef>

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

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

#include "lib/jxl/enc_gamma_correct.h"

#include "lib/jxl/enc_image_bundle.h"

namespace jxl {

namespace {

// color is linear, but blending happens in gamma-compressed space using

// (gamma-compressed) grayscale background color, alpha image represents

// weights of the sRGB colors in the [0 .. (1 << bit_depth) - 1] interval,

// output image is in linear space.

void AlphaBlend(const Image3F& in, const size_t c, float background_linear,

                const ImageF& alpha, Image3F* out) {

  const float background = LinearToSrgb8Direct(background_linear);

  for (size_t y = 0; y < out->ysize(); ++y) {

    const float* JXL_RESTRICT row_a = alpha.ConstRow(y);

    const float* JXL_RESTRICT row_i = in.ConstPlaneRow(c, y);

    float* JXL_RESTRICT row_o = out->PlaneRow(c, y);

    for (size_t x = 0; x < out->xsize(); ++x) {

      const float a = row_a[x];

      if (a <= 0.f) {

        row_o[x] = background_linear;

      } else if (a >= 1.f) {

        row_o[x] = row_i[x];

      } else {

        const float w_fg = a;

        const float w_bg = 1.0f - w_fg;

        const float fg = w_fg * LinearToSrgb8Direct(row_i[x]);

        const float bg = w_bg * background;

        row_o[x] = Srgb8ToLinearDirect(fg + bg);

void AlphaBlend(float background_linear, ImageBundle* io_linear_srgb) {

  // No alpha => all opaque.

  if (!io_linear_srgb->HasAlpha()) return;

  for (size_t c = 0; c < 3; ++c) {

    AlphaBlend(*io_linear_srgb->color(), c, background_linear,

               *io_linear_srgb->alpha(), io_linear_srgb->color());

Status ComputeScoreImpl(const ImageBundle& rgb0, const ImageBundle& rgb1,

                        Comparator* comparator, ImageF* distmap, float& score) {

  JXL_RETURN_IF_ERROR(comparator->SetReferenceImage(rgb0));

  JXL_RETURN_IF_ERROR(comparator->CompareWith(rgb1, distmap, &score));

  return true;

}  // namespace

Status ComputeScore(const ImageBundle& rgb0, const ImageBundle& rgb1,

                    Comparator* comparator, const JxlCmsInterface& cms,

                    float* score, ImageF* diffmap, ThreadPool* pool,

                    bool ignore_alpha) {

  JxlMemoryManager* memory_manager = rgb0.memory_manager();

  // Convert to linear sRGB (unless already in that space)

  ImageMetadata metadata0 = *rgb0.metadata();

  ImageBundle store0(memory_manager, &metadata0);

  const ImageBundle* linear_srgb0;

  JXL_RETURN_IF_ERROR(

      TransformIfNeeded(rgb0, ColorEncoding::LinearSRGB(rgb0.IsGray()), cms,

                        pool, &store0, &linear_srgb0));

  ImageMetadata metadata1 = *rgb1.metadata();

  ImageBundle store1(memory_manager, &metadata1);

  const ImageBundle* linear_srgb1;

  JXL_RETURN_IF_ERROR(

      TransformIfNeeded(rgb1, ColorEncoding::LinearSRGB(rgb1.IsGray()), cms,

                        pool, &store1, &linear_srgb1));

  // No alpha: skip blending, only need a single call to Butteraugli.

  if (ignore_alpha || (!rgb0.HasAlpha() && !rgb1.HasAlpha())) {

    JXL_RETURN_IF_ERROR(ComputeScoreImpl(*linear_srgb0, *linear_srgb1,

                                         comparator, diffmap, *score));

    return true;

  // Blend on black and white backgrounds

  const float black = 0.0f;

  JXL_ASSIGN_OR_RETURN(ImageBundle blended_black0, linear_srgb0->Copy());

  JXL_ASSIGN_OR_RETURN(ImageBundle blended_black1, linear_srgb1->Copy());

  AlphaBlend(black, &blended_black0);

  AlphaBlend(black, &blended_black1);

  const float white = 1.0f;

  JXL_ASSIGN_OR_RETURN(ImageBundle blended_white0, linear_srgb0->Copy());

  JXL_ASSIGN_OR_RETURN(ImageBundle blended_white1, linear_srgb1->Copy());

  AlphaBlend(white, &blended_white0);

  AlphaBlend(white, &blended_white1);

  ImageF diffmap_black;

  ImageF diffmap_white;

  float dist_black;

  JXL_RETURN_IF_ERROR(ComputeScoreImpl(blended_black0, blended_black1,

                                       comparator, &diffmap_black, dist_black));

  float dist_white;

  JXL_RETURN_IF_ERROR(ComputeScoreImpl(blended_white0, blended_white1,

                                       comparator, &diffmap_white, dist_white));

  // diffmap and return values are the max of diffmap_black/white.

  if (diffmap != nullptr) {

    const size_t xsize = rgb0.xsize();

    const size_t ysize = rgb0.ysize();

    JXL_ASSIGN_OR_RETURN(*diffmap,

                         ImageF::Create(memory_manager, xsize, ysize));

    for (size_t y = 0; y < ysize; ++y) {

      const float* JXL_RESTRICT row_black = diffmap_black.ConstRow(y);

      const float* JXL_RESTRICT row_white = diffmap_white.ConstRow(y);

      float* JXL_RESTRICT row_out = diffmap->Row(y);

      for (size_t x = 0; x < xsize; ++x) {

        row_out[x] = std::max(row_black[x], row_white[x]);

  *score = std::max(dist_black, dist_white);

  return true;

}  // namespace jxl