| // 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 "src/utils/quant_levels_dec_utils.h" |
| |
| #include <string.h> // for memset |
| |
| #include "src/utils/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_8b_MASK (int)(~0U << (8 + DFIX)) |
| static WEBP_INLINE uint8_t clip_8b(int v) { |
| return (!(v & CLIP_8b_MASK)) ? (uint8_t)(v >> DFIX) : (v < 0) ? 0u : 255u; |
| } |
| #undef CLIP_8b_MASK |
| |
| // 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) { |
| int radius = 4 * strength / 100; |
| |
| if (strength < 0 || strength > 100) return 0; |
| if (data == NULL || width <= 0 || height <= 0) return 0; // bad params |
| |
| // limit the filter size to not exceed the image dimensions |
| if (2 * radius + 1 > width) radius = (width - 1) >> 1; |
| if (2 * radius + 1 > height) radius = (height - 1) >> 1; |
| |
| 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; |
| } |