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+// 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.
+//
+// Author: Jyrki Alakuijala (jyrki.alakuijala@gmail.com)
+
+#ifndef LIB_JXL_BUTTERAUGLI_BUTTERAUGLI_H_
+#define LIB_JXL_BUTTERAUGLI_BUTTERAUGLI_H_
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <atomic>
+#include <cmath>
+#include <memory>
+#include <vector>
+
+#include "lib/jxl/base/compiler_specific.h"
+#include "lib/jxl/common.h"
+#include "lib/jxl/image.h"
+#include "lib/jxl/image_ops.h"
+
+#define BUTTERAUGLI_ENABLE_CHECKS 0
+#define BUTTERAUGLI_RESTRICT JXL_RESTRICT
+
+// This is the main interface to butteraugli image similarity
+// analysis function.
+
+namespace jxl {
+
+struct ButteraugliParams {
+  // Multiplier for penalizing new HF artifacts more than blurring away
+  // features. 1.0=neutral.
+  float hf_asymmetry = 1.0f;
+
+  // Multiplier for the psychovisual difference in the X channel.
+  float xmul = 1.0f;
+
+  // Number of nits that correspond to 1.0f input values.
+  float intensity_target = 80.0f;
+};
+
+// ButteraugliInterface defines the public interface for butteraugli.
+//
+// It calculates the difference between rgb0 and rgb1.
+//
+// rgb0 and rgb1 contain the images. rgb0[c][px] and rgb1[c][px] contains
+// the red image for c == 0, green for c == 1, blue for c == 2. Location index
+// px is calculated as y * xsize + x.
+//
+// Value of pixels of images rgb0 and rgb1 need to be represented as raw
+// intensity. Most image formats store gamma corrected intensity in pixel
+// values. This gamma correction has to be removed, by applying the following
+// function to values in the 0-1 range:
+// butteraugli_val = pow(input_val, gamma);
+// A typical value of gamma is 2.2. It is usually stored in the image header.
+// Take care not to confuse that value with its inverse. The gamma value should
+// be always greater than one.
+// Butteraugli does not work as intended if the caller does not perform
+// gamma correction.
+//
+// hf_asymmetry is a multiplier for penalizing new HF artifacts more than
+// blurring away features (1.0 -> neutral).
+//
+// diffmap will contain an image of the size xsize * ysize, containing
+// localized differences for values px (indexed with the px the same as rgb0
+// and rgb1). diffvalue will give a global score of similarity.
+//
+// A diffvalue smaller than kButteraugliGood indicates that images can be
+// observed as the same image.
+// diffvalue larger than kButteraugliBad indicates that a difference between
+// the images can be observed.
+// A diffvalue between kButteraugliGood and kButteraugliBad indicates that
+// a subtle difference can be observed between the images.
+//
+// Returns true on success.
+bool ButteraugliInterface(const Image3F &rgb0, const Image3F &rgb1,
+                          const ButteraugliParams &params, ImageF &diffmap,
+                          double &diffvalue);
+
+// Deprecated (calls the previous function)
+bool ButteraugliInterface(const Image3F &rgb0, const Image3F &rgb1,
+                          float hf_asymmetry, float xmul, ImageF &diffmap,
+                          double &diffvalue);
+
+// Converts the butteraugli score into fuzzy class values that are continuous
+// at the class boundary. The class boundary location is based on human
+// raters, but the slope is arbitrary. Particularly, it does not reflect
+// the expectation value of probabilities of the human raters. It is just
+// expected that a smoother class boundary will allow for higher-level
+// optimization algorithms to work faster.
+//
+// Returns 2.0 for a perfect match, and 1.0 for 'ok', 0.0 for bad. Because the
+// scoring is fuzzy, a butteraugli score of 0.96 would return a class of
+// around 1.9.
+double ButteraugliFuzzyClass(double score);
+
+// Input values should be in range 0 (bad) to 2 (good). Use
+// kButteraugliNormalization as normalization.
+double ButteraugliFuzzyInverse(double seek);
+
+// Implementation details, don't use anything below or your code will
+// break in the future.
+
+#ifdef _MSC_VER
+#define BUTTERAUGLI_INLINE __forceinline
+#else
+#define BUTTERAUGLI_INLINE inline
+#endif
+
+#ifdef __clang__
+// Early versions of Clang did not support __builtin_assume_aligned.
+#define BUTTERAUGLI_HAS_ASSUME_ALIGNED __has_builtin(__builtin_assume_aligned)
+#elif defined(__GNUC__)
+#define BUTTERAUGLI_HAS_ASSUME_ALIGNED 1
+#else
+#define BUTTERAUGLI_HAS_ASSUME_ALIGNED 0
+#endif
+
+// Returns a void* pointer which the compiler then assumes is N-byte aligned.
+// Example: float* JXL_RESTRICT aligned = (float*)JXL_ASSUME_ALIGNED(in, 32);
+//
+// The assignment semantics are required by GCC/Clang. ICC provides an in-place
+// __assume_aligned, whereas MSVC's __assume appears unsuitable.
+#if BUTTERAUGLI_HAS_ASSUME_ALIGNED
+#define BUTTERAUGLI_ASSUME_ALIGNED(ptr, align) \
+  __builtin_assume_aligned((ptr), (align))
+#else
+#define BUTTERAUGLI_ASSUME_ALIGNED(ptr, align) (ptr)
+#endif  // BUTTERAUGLI_HAS_ASSUME_ALIGNED
+
+struct PsychoImage {
+  ImageF uhf[2];  // XY
+  ImageF hf[2];   // XY
+  Image3F mf;     // XYB
+  Image3F lf;     // XYB
+};
+
+// Blur needs a transposed image.
+// Hold it here and only allocate on demand to reduce memory usage.
+struct BlurTemp {
+  ImageF *GetTransposed(const ImageF &in) {
+    if (transposed_temp.xsize() == 0) {
+      transposed_temp = ImageF(in.ysize(), in.xsize());
+    }
+    return &transposed_temp;
+  }
+
+  ImageF transposed_temp;
+};
+
+class ButteraugliComparator {
+ public:
+  // Butteraugli is calibrated at xmul = 1.0. We add a multiplier here so that
+  // we can test the hypothesis that a higher weighing of the X channel would
+  // improve results at higher Butteraugli values.
+  ButteraugliComparator(const Image3F &rgb0, const ButteraugliParams &params);
+  virtual ~ButteraugliComparator() = default;
+
+  // Computes the butteraugli map between the original image given in the
+  // constructor and the distorted image give here.
+  void Diffmap(const Image3F &rgb1, ImageF &result) const;
+
+  // Same as above, but OpsinDynamicsImage() was already applied.
+  void DiffmapOpsinDynamicsImage(const Image3F &xyb1, ImageF &result) const;
+
+  // Same as above, but the frequency decomposition was already applied.
+  void DiffmapPsychoImage(const PsychoImage &pi1, ImageF &diffmap) const;
+
+  void Mask(ImageF *BUTTERAUGLI_RESTRICT mask) const;
+
+ private:
+  Image3F *Temp() const;
+  void ReleaseTemp() const;
+
+  const size_t xsize_;
+  const size_t ysize_;
+  ButteraugliParams params_;
+  PsychoImage pi0_;
+
+  // Shared temporary image storage to reduce the number of allocations;
+  // obtained via Temp(), must call ReleaseTemp when no longer needed.
+  mutable Image3F temp_;
+  mutable std::atomic_flag temp_in_use_ = ATOMIC_FLAG_INIT;
+
+  mutable BlurTemp blur_temp_;
+  std::unique_ptr<ButteraugliComparator> sub_;
+};
+
+// Deprecated.
+bool ButteraugliDiffmap(const Image3F &rgb0, const Image3F &rgb1,
+                        double hf_asymmetry, double xmul, ImageF &diffmap);
+
+bool ButteraugliDiffmap(const Image3F &rgb0, const Image3F &rgb1,
+                        const ButteraugliParams &params, ImageF &diffmap);
+
+double ButteraugliScoreFromDiffmap(const ImageF &diffmap,
+                                   const ButteraugliParams *params = nullptr);
+
+// Generate rgb-representation of the distance between two images.
+Image3F CreateHeatMapImage(const ImageF &distmap, double good_threshold,
+                           double bad_threshold);
+
+}  // namespace jxl
+
+#endif  // LIB_JXL_BUTTERAUGLI_BUTTERAUGLI_H_