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diff --git a/src/utils/palette.h b/src/utils/palette.h
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+// Copyright 2023 Google Inc. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+// -----------------------------------------------------------------------------
+//
+// Utilities for palette analysis.
+//
+// Author: Vincent Rabaud (vrabaud@google.com)
+
+#ifndef WEBP_UTILS_PALETTE_H_
+#define WEBP_UTILS_PALETTE_H_
+
+#include "src/webp/types.h"
+
+struct WebPPicture;
+
+// The different ways a palette can be sorted.
+typedef enum PaletteSorting {
+  kSortedDefault = 0,
+  // Sorts by minimizing L1 deltas between consecutive colors, giving more
+  // weight to RGB colors.
+  kMinimizeDelta = 1,
+  // Implements the modified Zeng method from "A Survey on Palette Reordering
+  // Methods for Improving the Compression of Color-Indexed Images" by Armando
+  // J. Pinho and Antonio J. R. Neves.
+  kModifiedZeng = 2,
+  kUnusedPalette = 3,
+  kPaletteSortingNum = 4
+} PaletteSorting;
+
+// Returns the index of 'color' in the sorted palette 'sorted' of size
+// 'num_colors'.
+int SearchColorNoIdx(const uint32_t sorted[], uint32_t color, int num_colors);
+
+// Sort palette in increasing order and prepare an inverse mapping array.
+void PrepareMapToPalette(const uint32_t palette[], uint32_t num_colors,
+                         uint32_t sorted[], uint32_t idx_map[]);
+
+// Returns count of unique colors in 'pic', assuming pic->use_argb is true.
+// If the unique color count is more than MAX_PALETTE_SIZE, returns
+// MAX_PALETTE_SIZE+1.
+// If 'palette' is not NULL and the number of unique colors is less than or
+// equal to MAX_PALETTE_SIZE, also outputs the actual unique colors into
+// 'palette' in a sorted order. Note: 'palette' is assumed to be an array
+// already allocated with at least MAX_PALETTE_SIZE elements.
+int GetColorPalette(const struct WebPPicture* const pic,
+                    uint32_t* const palette);
+
+// Sorts the palette according to the criterion defined by 'method'.
+// 'palette_sorted' is the input palette sorted lexicographically, as done in
+// PrepareMapToPalette. Returns 0 on memory allocation error.
+int PaletteSort(PaletteSorting method, const struct WebPPicture* const pic,
+                const uint32_t* const palette_sorted, uint32_t num_colors,
+                uint32_t* const palette);
+
+#endif  // WEBP_UTILS_PALETTE_H_