palette.h (2660B)
1 // Copyright 2023 Google Inc. All Rights Reserved. 2 // 3 // Use of this source code is governed by a BSD-style license 4 // that can be found in the COPYING file in the root of the source 5 // tree. An additional intellectual property rights grant can be found 6 // in the file PATENTS. All contributing project authors may 7 // be found in the AUTHORS file in the root of the source tree. 8 // ----------------------------------------------------------------------------- 9 // 10 // Utilities for palette analysis. 11 // 12 // Author: Vincent Rabaud (vrabaud@google.com) 13 14 #ifndef WEBP_UTILS_PALETTE_H_ 15 #define WEBP_UTILS_PALETTE_H_ 16 17 #include "src/webp/types.h" 18 19 struct WebPPicture; 20 21 // The different ways a palette can be sorted. 22 typedef enum PaletteSorting { 23 kSortedDefault = 0, 24 // Sorts by minimizing L1 deltas between consecutive colors, giving more 25 // weight to RGB colors. 26 kMinimizeDelta = 1, 27 // Implements the modified Zeng method from "A Survey on Palette Reordering 28 // Methods for Improving the Compression of Color-Indexed Images" by Armando 29 // J. Pinho and Antonio J. R. Neves. 30 kModifiedZeng = 2, 31 kUnusedPalette = 3, 32 kPaletteSortingNum = 4 33 } PaletteSorting; 34 35 // Returns the index of 'color' in the sorted palette 'sorted' of size 36 // 'num_colors'. 37 int SearchColorNoIdx(const uint32_t sorted[], uint32_t color, int num_colors); 38 39 // Sort palette in increasing order and prepare an inverse mapping array. 40 void PrepareMapToPalette(const uint32_t palette[], uint32_t num_colors, 41 uint32_t sorted[], uint32_t idx_map[]); 42 43 // Returns count of unique colors in 'pic', assuming pic->use_argb is true. 44 // If the unique color count is more than MAX_PALETTE_SIZE, returns 45 // MAX_PALETTE_SIZE+1. 46 // If 'palette' is not NULL and the number of unique colors is less than or 47 // equal to MAX_PALETTE_SIZE, also outputs the actual unique colors into 48 // 'palette' in a sorted order. Note: 'palette' is assumed to be an array 49 // already allocated with at least MAX_PALETTE_SIZE elements. 50 int GetColorPalette(const struct WebPPicture* const pic, 51 uint32_t* const palette); 52 53 // Sorts the palette according to the criterion defined by 'method'. 54 // 'palette_sorted' is the input palette sorted lexicographically, as done in 55 // PrepareMapToPalette. Returns 0 on memory allocation error. 56 // For kSortedDefault and kMinimizeDelta methods, 0 (if present) is set as the 57 // last element to optimize later storage. 58 int PaletteSort(PaletteSorting method, const struct WebPPicture* const pic, 59 const uint32_t* const palette_sorted, uint32_t num_colors, 60 uint32_t* const palette); 61 62 #endif // WEBP_UTILS_PALETTE_H_