| // Copyright 2011 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. |
| // ----------------------------------------------------------------------------- |
| // |
| // filter estimation |
| // |
| // Author: Urvang (urvang@google.com) |
| |
| #include "src/utils/filters_utils.h" |
| #include <stdlib.h> |
| #include <string.h> |
| |
| // ----------------------------------------------------------------------------- |
| // Quick estimate of a potentially interesting filter mode to try. |
| |
| #define SMAX 16 |
| #define SDIFF(a, b) (abs((a) - (b)) >> 4) // Scoring diff, in [0..SMAX) |
| |
| static WEBP_INLINE int GradientPredictor(uint8_t a, uint8_t b, uint8_t c) { |
| const int g = a + b - c; |
| return ((g & ~0xff) == 0) ? g : (g < 0) ? 0 : 255; // clip to 8bit |
| } |
| |
| WEBP_FILTER_TYPE WebPEstimateBestFilter(const uint8_t* data, |
| int width, int height, int stride) { |
| int i, j; |
| int bins[WEBP_FILTER_LAST][SMAX]; |
| memset(bins, 0, sizeof(bins)); |
| |
| // We only sample every other pixels. That's enough. |
| for (j = 2; j < height - 1; j += 2) { |
| const uint8_t* const p = data + j * stride; |
| int mean = p[0]; |
| for (i = 2; i < width - 1; i += 2) { |
| const int diff0 = SDIFF(p[i], mean); |
| const int diff1 = SDIFF(p[i], p[i - 1]); |
| const int diff2 = SDIFF(p[i], p[i - width]); |
| const int grad_pred = |
| GradientPredictor(p[i - 1], p[i - width], p[i - width - 1]); |
| const int diff3 = SDIFF(p[i], grad_pred); |
| bins[WEBP_FILTER_NONE][diff0] = 1; |
| bins[WEBP_FILTER_HORIZONTAL][diff1] = 1; |
| bins[WEBP_FILTER_VERTICAL][diff2] = 1; |
| bins[WEBP_FILTER_GRADIENT][diff3] = 1; |
| mean = (3 * mean + p[i] + 2) >> 2; |
| } |
| } |
| { |
| int filter; |
| WEBP_FILTER_TYPE best_filter = WEBP_FILTER_NONE; |
| int best_score = 0x7fffffff; |
| for (filter = WEBP_FILTER_NONE; filter < WEBP_FILTER_LAST; ++filter) { |
| int score = 0; |
| for (i = 0; i < SMAX; ++i) { |
| if (bins[filter][i] > 0) { |
| score += i; |
| } |
| } |
| if (score < best_score) { |
| best_score = score; |
| best_filter = (WEBP_FILTER_TYPE)filter; |
| } |
| } |
| return best_filter; |
| } |
| } |
| |
| #undef SMAX |
| #undef SDIFF |
| |
| //------------------------------------------------------------------------------ |