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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.
+
+#ifndef LIB_JXL_ENC_COMPARATOR_H_
+#define LIB_JXL_ENC_COMPARATOR_H_
+
+#include "lib/jxl/base/data_parallel.h"
+#include "lib/jxl/base/status.h"
+#include "lib/jxl/image.h"
+#include "lib/jxl/image_bundle.h"
+
+namespace jxl {
+
+class Comparator {
+ public:
+  virtual ~Comparator() = default;
+
+  // Sets the reference image, the first to compare
+  // Image must be in linear sRGB (gamma expanded) in range 0.0f-1.0f as
+  // the range from standard black point to standard white point, but values
+  // outside permitted.
+  virtual Status SetReferenceImage(const ImageBundle& ref) = 0;
+
+  // Sets the actual image (with loss), the second to compare
+  // Image must be in linear sRGB (gamma expanded) in range 0.0f-1.0f as
+  // the range from standard black point to standard white point, but values
+  // outside permitted.
+  // In diffmap it outputs the local score per pixel, while in score it outputs
+  // a single score. Any one may be set to nullptr to not compute it.
+  virtual Status CompareWith(const ImageBundle& actual, ImageF* diffmap,
+                             float* score) = 0;
+
+  // Quality thresholds for diffmap and score values.
+  // The good score must represent a value where the images are considered to
+  // be perceptually indistinguishable (but not identical)
+  // The bad value must be larger than good to indicate "lower means better"
+  // and smaller than good to indicate "higher means better"
+  virtual float GoodQualityScore() const = 0;
+  virtual float BadQualityScore() const = 0;
+};
+
+// Computes the score given images in any RGB color model, optionally with
+// alpha channel.
+float ComputeScore(const ImageBundle& rgb0, const ImageBundle& rgb1,
+                   Comparator* comparator, const JxlCmsInterface& cms,
+                   ImageF* diffmap = nullptr, ThreadPool* pool = nullptr);
+
+}  // namespace jxl
+
+#endif  // LIB_JXL_ENC_COMPARATOR_H_