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