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Diffstat (limited to 'media/libwebp/utils/quant_levels_dec_utils.c')
| -rw-r--r-- | media/libwebp/utils/quant_levels_dec_utils.c | 284 |
1 files changed, 284 insertions, 0 deletions
diff --git a/media/libwebp/utils/quant_levels_dec_utils.c b/media/libwebp/utils/quant_levels_dec_utils.c new file mode 100644 index 000000000..d4d23d314 --- /dev/null +++ b/media/libwebp/utils/quant_levels_dec_utils.c @@ -0,0 +1,284 @@ +// Copyright 2013 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. +// ----------------------------------------------------------------------------- +// +// Implement gradient smoothing: we replace a current alpha value by its +// surrounding average if it's close enough (that is: the change will be less +// than the minimum distance between two quantized level). +// We use sliding window for computing the 2d moving average. +// +// Author: Skal (pascal.massimino@gmail.com) + +#include "./quant_levels_dec_utils.h" + +#include <string.h> // for memset + +#include "./utils.h" + +// #define USE_DITHERING // uncomment to enable ordered dithering (not vital) + +#define FIX 16 // fix-point precision for averaging +#define LFIX 2 // extra precision for look-up table +#define LUT_SIZE ((1 << (8 + LFIX)) - 1) // look-up table size + +#if defined(USE_DITHERING) + +#define DFIX 4 // extra precision for ordered dithering +#define DSIZE 4 // dithering size (must be a power of two) +// cf. http://en.wikipedia.org/wiki/Ordered_dithering +static const uint8_t kOrderedDither[DSIZE][DSIZE] = { + { 0, 8, 2, 10 }, // coefficients are in DFIX fixed-point precision + { 12, 4, 14, 6 }, + { 3, 11, 1, 9 }, + { 15, 7, 13, 5 } +}; + +#else +#define DFIX 0 +#endif + +typedef struct { + int width_, height_; // dimension + int stride_; // stride in bytes + int row_; // current input row being processed + uint8_t* src_; // input pointer + uint8_t* dst_; // output pointer + + int radius_; // filter radius (=delay) + int scale_; // normalization factor, in FIX bits precision + + void* mem_; // all memory + + // various scratch buffers + uint16_t* start_; + uint16_t* cur_; + uint16_t* end_; + uint16_t* top_; + uint16_t* average_; + + // input levels distribution + int num_levels_; // number of quantized levels + int min_, max_; // min and max level values + int min_level_dist_; // smallest distance between two consecutive levels + + int16_t* correction_; // size = 1 + 2*LUT_SIZE -> ~4k memory +} SmoothParams; + +//------------------------------------------------------------------------------ + +#define CLIP_MASK (int)(~0U << (8 + DFIX)) +static WEBP_INLINE uint8_t clip_8b(int v) { + return (!(v & CLIP_MASK)) ? (uint8_t)(v >> DFIX) : (v < 0) ? 0u : 255u; +} + +// vertical accumulation +static void VFilter(SmoothParams* const p) { + const uint8_t* src = p->src_; + const int w = p->width_; + uint16_t* const cur = p->cur_; + const uint16_t* const top = p->top_; + uint16_t* const out = p->end_; + uint16_t sum = 0; // all arithmetic is modulo 16bit + int x; + + for (x = 0; x < w; ++x) { + uint16_t new_value; + sum += src[x]; + new_value = top[x] + sum; + out[x] = new_value - cur[x]; // vertical sum of 'r' pixels. + cur[x] = new_value; + } + // move input pointers one row down + p->top_ = p->cur_; + p->cur_ += w; + if (p->cur_ == p->end_) p->cur_ = p->start_; // roll-over + // We replicate edges, as it's somewhat easier as a boundary condition. + // That's why we don't update the 'src' pointer on top/bottom area: + if (p->row_ >= 0 && p->row_ < p->height_ - 1) { + p->src_ += p->stride_; + } +} + +// horizontal accumulation. We use mirror replication of missing pixels, as it's +// a little easier to implement (surprisingly). +static void HFilter(SmoothParams* const p) { + const uint16_t* const in = p->end_; + uint16_t* const out = p->average_; + const uint32_t scale = p->scale_; + const int w = p->width_; + const int r = p->radius_; + + int x; + for (x = 0; x <= r; ++x) { // left mirroring + const uint16_t delta = in[x + r - 1] + in[r - x]; + out[x] = (delta * scale) >> FIX; + } + for (; x < w - r; ++x) { // bulk middle run + const uint16_t delta = in[x + r] - in[x - r - 1]; + out[x] = (delta * scale) >> FIX; + } + for (; x < w; ++x) { // right mirroring + const uint16_t delta = + 2 * in[w - 1] - in[2 * w - 2 - r - x] - in[x - r - 1]; + out[x] = (delta * scale) >> FIX; + } +} + +// emit one filtered output row +static void ApplyFilter(SmoothParams* const p) { + const uint16_t* const average = p->average_; + const int w = p->width_; + const int16_t* const correction = p->correction_; +#if defined(USE_DITHERING) + const uint8_t* const dither = kOrderedDither[p->row_ % DSIZE]; +#endif + uint8_t* const dst = p->dst_; + int x; + for (x = 0; x < w; ++x) { + const int v = dst[x]; + if (v < p->max_ && v > p->min_) { + const int c = (v << DFIX) + correction[average[x] - (v << LFIX)]; +#if defined(USE_DITHERING) + dst[x] = clip_8b(c + dither[x % DSIZE]); +#else + dst[x] = clip_8b(c); +#endif + } + } + p->dst_ += p->stride_; // advance output pointer +} + +//------------------------------------------------------------------------------ +// Initialize correction table + +static void InitCorrectionLUT(int16_t* const lut, int min_dist) { + // The correction curve is: + // f(x) = x for x <= threshold2 + // f(x) = 0 for x >= threshold1 + // and a linear interpolation for range x=[threshold2, threshold1] + // (along with f(-x) = -f(x) symmetry). + // Note that: threshold2 = 3/4 * threshold1 + const int threshold1 = min_dist << LFIX; + const int threshold2 = (3 * threshold1) >> 2; + const int max_threshold = threshold2 << DFIX; + const int delta = threshold1 - threshold2; + int i; + for (i = 1; i <= LUT_SIZE; ++i) { + int c = (i <= threshold2) ? (i << DFIX) + : (i < threshold1) ? max_threshold * (threshold1 - i) / delta + : 0; + c >>= LFIX; + lut[+i] = +c; + lut[-i] = -c; + } + lut[0] = 0; +} + +static void CountLevels(SmoothParams* const p) { + int i, j, last_level; + uint8_t used_levels[256] = { 0 }; + const uint8_t* data = p->src_; + p->min_ = 255; + p->max_ = 0; + for (j = 0; j < p->height_; ++j) { + for (i = 0; i < p->width_; ++i) { + const int v = data[i]; + if (v < p->min_) p->min_ = v; + if (v > p->max_) p->max_ = v; + used_levels[v] = 1; + } + data += p->stride_; + } + // Compute the mininum distance between two non-zero levels. + p->min_level_dist_ = p->max_ - p->min_; + last_level = -1; + for (i = 0; i < 256; ++i) { + if (used_levels[i]) { + ++p->num_levels_; + if (last_level >= 0) { + const int level_dist = i - last_level; + if (level_dist < p->min_level_dist_) { + p->min_level_dist_ = level_dist; + } + } + last_level = i; + } + } +} + +// Initialize all params. +static int InitParams(uint8_t* const data, int width, int height, int stride, + int radius, SmoothParams* const p) { + const int R = 2 * radius + 1; // total size of the kernel + + const size_t size_scratch_m = (R + 1) * width * sizeof(*p->start_); + const size_t size_m = width * sizeof(*p->average_); + const size_t size_lut = (1 + 2 * LUT_SIZE) * sizeof(*p->correction_); + const size_t total_size = size_scratch_m + size_m + size_lut; + uint8_t* mem = (uint8_t*)WebPSafeMalloc(1U, total_size); + + if (mem == NULL) return 0; + p->mem_ = (void*)mem; + + p->start_ = (uint16_t*)mem; + p->cur_ = p->start_; + p->end_ = p->start_ + R * width; + p->top_ = p->end_ - width; + memset(p->top_, 0, width * sizeof(*p->top_)); + mem += size_scratch_m; + + p->average_ = (uint16_t*)mem; + mem += size_m; + + p->width_ = width; + p->height_ = height; + p->stride_ = stride; + p->src_ = data; + p->dst_ = data; + p->radius_ = radius; + p->scale_ = (1 << (FIX + LFIX)) / (R * R); // normalization constant + p->row_ = -radius; + + // analyze the input distribution so we can best-fit the threshold + CountLevels(p); + + // correction table + p->correction_ = ((int16_t*)mem) + LUT_SIZE; + InitCorrectionLUT(p->correction_, p->min_level_dist_); + + return 1; +} + +static void CleanupParams(SmoothParams* const p) { + WebPSafeFree(p->mem_); +} + +int WebPDequantizeLevels(uint8_t* const data, int width, int height, int stride, + int strength) { + const int radius = 4 * strength / 100; + if (strength < 0 || strength > 100) return 0; + if (data == NULL || width <= 0 || height <= 0) return 0; // bad params + if (radius > 0) { + SmoothParams p; + memset(&p, 0, sizeof(p)); + if (!InitParams(data, width, height, stride, radius, &p)) return 0; + if (p.num_levels_ > 2) { + for (; p.row_ < p.height_; ++p.row_) { + VFilter(&p); // accumulate average of input + // Need to wait few rows in order to prime the filter, + // before emitting some output. + if (p.row_ >= p.radius_) { + HFilter(&p); + ApplyFilter(&p); + } + } + } + CleanupParams(&p); + } + return 1; +} |