summaryrefslogtreecommitdiffstats
path: root/media/libwebp/utils/quant_levels_dec_utils.c
blob: d4d23d314723e5145c0017f65c19aeb026bc2f4b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
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;
}