filters_utils.c (2588B)
1 // Copyright 2011 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 // filter estimation 11 // 12 // Author: Urvang (urvang@google.com) 13 14 #include <stdlib.h> 15 #include <string.h> 16 17 #include "src/dsp/dsp.h" 18 #include "src/webp/types.h" 19 #include "src/utils/filters_utils.h" 20 21 // ----------------------------------------------------------------------------- 22 // Quick estimate of a potentially interesting filter mode to try. 23 24 #define SMAX 16 25 #define SDIFF(a, b) (abs((a) - (b)) >> 4) // Scoring diff, in [0..SMAX) 26 27 static WEBP_INLINE int GradientPredictor(uint8_t a, uint8_t b, uint8_t c) { 28 const int g = a + b - c; 29 return ((g & ~0xff) == 0) ? g : (g < 0) ? 0 : 255; // clip to 8bit 30 } 31 32 WEBP_FILTER_TYPE WebPEstimateBestFilter(const uint8_t* data, 33 int width, int height, int stride) { 34 int i, j; 35 int bins[WEBP_FILTER_LAST][SMAX]; 36 memset(bins, 0, sizeof(bins)); 37 38 // We only sample every other pixels. That's enough. 39 for (j = 2; j < height - 1; j += 2) { 40 const uint8_t* const p = data + j * stride; 41 int mean = p[0]; 42 for (i = 2; i < width - 1; i += 2) { 43 const int diff0 = SDIFF(p[i], mean); 44 const int diff1 = SDIFF(p[i], p[i - 1]); 45 const int diff2 = SDIFF(p[i], p[i - width]); 46 const int grad_pred = 47 GradientPredictor(p[i - 1], p[i - width], p[i - width - 1]); 48 const int diff3 = SDIFF(p[i], grad_pred); 49 bins[WEBP_FILTER_NONE][diff0] = 1; 50 bins[WEBP_FILTER_HORIZONTAL][diff1] = 1; 51 bins[WEBP_FILTER_VERTICAL][diff2] = 1; 52 bins[WEBP_FILTER_GRADIENT][diff3] = 1; 53 mean = (3 * mean + p[i] + 2) >> 2; 54 } 55 } 56 { 57 int filter; 58 WEBP_FILTER_TYPE best_filter = WEBP_FILTER_NONE; 59 int best_score = 0x7fffffff; 60 for (filter = WEBP_FILTER_NONE; filter < WEBP_FILTER_LAST; ++filter) { 61 int score = 0; 62 for (i = 0; i < SMAX; ++i) { 63 if (bins[filter][i] > 0) { 64 score += i; 65 } 66 } 67 if (score < best_score) { 68 best_score = score; 69 best_filter = (WEBP_FILTER_TYPE)filter; 70 } 71 } 72 return best_filter; 73 } 74 } 75 76 #undef SMAX 77 #undef SDIFF 78 79 //------------------------------------------------------------------------------