diff options
Diffstat (limited to 'media/libwebp/utils/filters_utils.c')
-rw-r--r-- | media/libwebp/utils/filters_utils.c | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/media/libwebp/utils/filters_utils.c b/media/libwebp/utils/filters_utils.c new file mode 100644 index 000000000..49c1d18a2 --- /dev/null +++ b/media/libwebp/utils/filters_utils.c @@ -0,0 +1,76 @@ +// 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 "./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 + +//------------------------------------------------------------------------------ |