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// Copyright 2011 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
// Software License Agreement: http://www.webmproject.org/license/software/
// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// Spatial prediction using various filters
//
// Author: Urvang (urvang@google.com)
#include "./filters.h"
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
//------------------------------------------------------------------------------
// Helpful macro.
# define SANITY_CHECK(in, out) \
assert(in != NULL); \
assert(out != NULL); \
assert(width > 0); \
assert(height > 0); \
assert(bpp > 0); \
assert(stride >= width * bpp);
static WEBP_INLINE void PredictLine(const uint8_t* src, const uint8_t* pred,
uint8_t* dst, int length, int inverse) {
int i;
if (inverse) {
for (i = 0; i < length; ++i) dst[i] = src[i] + pred[i];
} else {
for (i = 0; i < length; ++i) dst[i] = src[i] - pred[i];
}
}
//------------------------------------------------------------------------------
// Horizontal filter.
static WEBP_INLINE void DoHorizontalFilter(const uint8_t* in,
int width, int height, int bpp, int stride, int inverse, uint8_t* out) {
int h;
const uint8_t* preds = (inverse ? out : in);
SANITY_CHECK(in, out);
// Filter line-by-line.
for (h = 0; h < height; ++h) {
// Leftmost pixel is predicted from above (except for topmost scanline).
if (h == 0) {
memcpy((void*)out, (const void*)in, bpp);
} else {
PredictLine(in, preds - stride, out, bpp, inverse);
}
PredictLine(in + bpp, preds, out + bpp, bpp * (width - 1), inverse);
preds += stride;
in += stride;
out += stride;
}
}
static void HorizontalFilter(const uint8_t* data, int width, int height,
int bpp, int stride, uint8_t* filtered_data) {
DoHorizontalFilter(data, width, height, bpp, stride, 0, filtered_data);
}
static void HorizontalUnfilter(const uint8_t* data, int width, int height,
int bpp, int stride, uint8_t* recon_data) {
DoHorizontalFilter(data, width, height, bpp, stride, 1, recon_data);
}
//------------------------------------------------------------------------------
// Vertical filter.
static WEBP_INLINE void DoVerticalFilter(const uint8_t* in,
int width, int height, int bpp, int stride, int inverse, uint8_t* out) {
int h;
const uint8_t* preds = (inverse ? out : in);
SANITY_CHECK(in, out);
// Very first top-left pixel is copied.
memcpy((void*)out, (const void*)in, bpp);
// Rest of top scan-line is left-predicted.
PredictLine(in + bpp, preds, out + bpp, bpp * (width - 1), inverse);
// Filter line-by-line.
for (h = 1; h < height; ++h) {
in += stride;
out += stride;
PredictLine(in, preds, out, bpp * width, inverse);
preds += stride;
}
}
static void VerticalFilter(const uint8_t* data, int width, int height,
int bpp, int stride, uint8_t* filtered_data) {
DoVerticalFilter(data, width, height, bpp, stride, 0, filtered_data);
}
static void VerticalUnfilter(const uint8_t* data, int width, int height,
int bpp, int stride, uint8_t* recon_data) {
DoVerticalFilter(data, width, height, bpp, stride, 1, recon_data);
}
//------------------------------------------------------------------------------
// Gradient filter.
static WEBP_INLINE int GradientPredictor(uint8_t a, uint8_t b, uint8_t c) {
const int g = a + b - c;
return (g < 0) ? 0 : (g > 255) ? 255 : g;
}
static WEBP_INLINE
void DoGradientFilter(const uint8_t* in, int width, int height,
int bpp, int stride, int inverse, uint8_t* out) {
const uint8_t* preds = (inverse ? out : in);
int h;
SANITY_CHECK(in, out);
// left prediction for top scan-line
memcpy((void*)out, (const void*)in, bpp);
PredictLine(in + bpp, preds, out + bpp, bpp * (width - 1), inverse);
// Filter line-by-line.
for (h = 1; h < height; ++h) {
int w;
preds += stride;
in += stride;
out += stride;
// leftmost pixel: predict from above.
PredictLine(in, preds - stride, out, bpp, inverse);
for (w = bpp; w < width * bpp; ++w) {
const int pred = GradientPredictor(preds[w - bpp],
preds[w - stride],
preds[w - stride - bpp]);
out[w] = in[w] + (inverse ? pred : -pred);
}
}
}
static void GradientFilter(const uint8_t* data, int width, int height,
int bpp, int stride, uint8_t* filtered_data) {
DoGradientFilter(data, width, height, bpp, stride, 0, filtered_data);
}
static void GradientUnfilter(const uint8_t* data, int width, int height,
int bpp, int stride, uint8_t* recon_data) {
DoGradientFilter(data, width, height, bpp, stride, 1, recon_data);
}
#undef SANITY_CHECK
// -----------------------------------------------------------------------------
// Quick estimate of a potentially interesting filter mode to try, in addition
// to the default NONE.
#define SMAX 16
#define SDIFF(a, b) (abs((a) - (b)) >> 4) // Scoring diff, in [0..SMAX)
WEBP_FILTER_TYPE EstimateBestFilter(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;
}
}
{
WEBP_FILTER_TYPE filter, 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 = filter;
}
}
return best_filter;
}
}
#undef SMAX
#undef SDIFF
//------------------------------------------------------------------------------
const WebPFilterFunc WebPFilters[WEBP_FILTER_LAST] = {
NULL, // WEBP_FILTER_NONE
HorizontalFilter, // WEBP_FILTER_HORIZONTAL
VerticalFilter, // WEBP_FILTER_VERTICAL
GradientFilter // WEBP_FILTER_GRADIENT
};
const WebPFilterFunc WebPUnfilters[WEBP_FILTER_LAST] = {
NULL, // WEBP_FILTER_NONE
HorizontalUnfilter, // WEBP_FILTER_HORIZONTAL
VerticalUnfilter, // WEBP_FILTER_VERTICAL
GradientUnfilter // WEBP_FILTER_GRADIENT
};
//------------------------------------------------------------------------------
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"
#endif
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