palette.h - mozsearch

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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_