1 // Copyright 2011 Google Inc. All Rights Reserved.
3 // This code is licensed under the same terms as WebM:
4 // Software License Agreement: http://www.webmproject.org/license/software/
5 // Additional IP Rights Grant: http://www.webmproject.org/license/additional/
6 // -----------------------------------------------------------------------------
8 // Spatial prediction using various filters
10 // Author: Urvang (urvang@google.com)
12 #include "./filters.h"
17 #if defined(__cplusplus) || defined(c_plusplus)
21 //------------------------------------------------------------------------------
24 # define SANITY_CHECK(in, out) \
26 assert(out != NULL); \
29 assert(stride >= width);
31 static WEBP_INLINE void PredictLine(const uint8_t* src, const uint8_t* pred,
32 uint8_t* dst, int length, int inverse) {
35 for (i = 0; i < length; ++i) dst[i] = src[i] + pred[i];
37 for (i = 0; i < length; ++i) dst[i] = src[i] - pred[i];
41 //------------------------------------------------------------------------------
44 static WEBP_INLINE void DoHorizontalFilter(const uint8_t* in,
45 int width, int height, int stride,
46 int inverse, uint8_t* out) {
48 const uint8_t* preds = (inverse ? out : in);
49 SANITY_CHECK(in, out);
51 // Filter line-by-line.
52 for (h = 0; h < height; ++h) {
53 // Leftmost pixel is predicted from above (except for topmost scanline).
57 PredictLine(in, preds - stride, out, 1, inverse);
59 PredictLine(in + 1, preds, out + 1, width - 1, inverse);
66 static void HorizontalFilter(const uint8_t* data, int width, int height,
67 int stride, uint8_t* filtered_data) {
68 DoHorizontalFilter(data, width, height, stride, 0, filtered_data);
71 static void HorizontalUnfilter(int width, int height, int stride,
73 DoHorizontalFilter(data, width, height, stride, 1, data);
76 //------------------------------------------------------------------------------
79 static WEBP_INLINE void DoVerticalFilter(const uint8_t* in,
80 int width, int height, int stride,
81 int inverse, uint8_t* out) {
83 const uint8_t* preds = (inverse ? out : in);
84 SANITY_CHECK(in, out);
86 // Very first top-left pixel is copied.
88 // Rest of top scan-line is left-predicted.
89 PredictLine(in + 1, preds, out + 1, width - 1, inverse);
91 // Filter line-by-line.
92 for (h = 1; h < height; ++h) {
95 PredictLine(in, preds, out, width, inverse);
100 static void VerticalFilter(const uint8_t* data, int width, int height,
101 int stride, uint8_t* filtered_data) {
102 DoVerticalFilter(data, width, height, stride, 0, filtered_data);
105 static void VerticalUnfilter(int width, int height, int stride, uint8_t* data) {
106 DoVerticalFilter(data, width, height, stride, 1, data);
109 //------------------------------------------------------------------------------
112 static WEBP_INLINE int GradientPredictor(uint8_t a, uint8_t b, uint8_t c) {
113 const int g = a + b - c;
114 return ((g & ~0xff) == 0) ? g : (g < 0) ? 0 : 255; // clip to 8bit
118 void DoGradientFilter(const uint8_t* in, int width, int height,
119 int stride, int inverse, uint8_t* out) {
120 const uint8_t* preds = (inverse ? out : in);
122 SANITY_CHECK(in, out);
124 // left prediction for top scan-line
126 PredictLine(in + 1, preds, out + 1, width - 1, inverse);
128 // Filter line-by-line.
129 for (h = 1; h < height; ++h) {
134 // leftmost pixel: predict from above.
135 PredictLine(in, preds - stride, out, 1, inverse);
136 for (w = 1; w < width; ++w) {
137 const int pred = GradientPredictor(preds[w - 1],
139 preds[w - stride - 1]);
140 out[w] = in[w] + (inverse ? pred : -pred);
145 static void GradientFilter(const uint8_t* data, int width, int height,
146 int stride, uint8_t* filtered_data) {
147 DoGradientFilter(data, width, height, stride, 0, filtered_data);
150 static void GradientUnfilter(int width, int height, int stride, uint8_t* data) {
151 DoGradientFilter(data, width, height, stride, 1, data);
156 // -----------------------------------------------------------------------------
157 // Quick estimate of a potentially interesting filter mode to try.
160 #define SDIFF(a, b) (abs((a) - (b)) >> 4) // Scoring diff, in [0..SMAX)
162 WEBP_FILTER_TYPE EstimateBestFilter(const uint8_t* data,
163 int width, int height, int stride) {
165 int bins[WEBP_FILTER_LAST][SMAX];
166 memset(bins, 0, sizeof(bins));
168 // We only sample every other pixels. That's enough.
169 for (j = 2; j < height - 1; j += 2) {
170 const uint8_t* const p = data + j * stride;
172 for (i = 2; i < width - 1; i += 2) {
173 const int diff0 = SDIFF(p[i], mean);
174 const int diff1 = SDIFF(p[i], p[i - 1]);
175 const int diff2 = SDIFF(p[i], p[i - width]);
176 const int grad_pred =
177 GradientPredictor(p[i - 1], p[i - width], p[i - width - 1]);
178 const int diff3 = SDIFF(p[i], grad_pred);
179 bins[WEBP_FILTER_NONE][diff0] = 1;
180 bins[WEBP_FILTER_HORIZONTAL][diff1] = 1;
181 bins[WEBP_FILTER_VERTICAL][diff2] = 1;
182 bins[WEBP_FILTER_GRADIENT][diff3] = 1;
183 mean = (3 * mean + p[i] + 2) >> 2;
187 WEBP_FILTER_TYPE filter, best_filter = WEBP_FILTER_NONE;
188 int best_score = 0x7fffffff;
189 for (filter = WEBP_FILTER_NONE; filter < WEBP_FILTER_LAST; ++filter) {
191 for (i = 0; i < SMAX; ++i) {
192 if (bins[filter][i] > 0) {
196 if (score < best_score) {
198 best_filter = filter;
208 //------------------------------------------------------------------------------
210 const WebPFilterFunc WebPFilters[WEBP_FILTER_LAST] = {
211 NULL, // WEBP_FILTER_NONE
212 HorizontalFilter, // WEBP_FILTER_HORIZONTAL
213 VerticalFilter, // WEBP_FILTER_VERTICAL
214 GradientFilter // WEBP_FILTER_GRADIENT
217 const WebPUnfilterFunc WebPUnfilters[WEBP_FILTER_LAST] = {
218 NULL, // WEBP_FILTER_NONE
219 HorizontalUnfilter, // WEBP_FILTER_HORIZONTAL
220 VerticalUnfilter, // WEBP_FILTER_VERTICAL
221 GradientUnfilter // WEBP_FILTER_GRADIENT
224 //------------------------------------------------------------------------------
226 #if defined(__cplusplus) || defined(c_plusplus)