libwebp-0.6.0-rc1

third_party/libwebp/utils/filters.c

-// 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.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
-
-//------------------------------------------------------------------------------