Statistics
| Branch: | Revision:

ffmpeg / libavcodec / elbg.c @ 2912e87a

History | View | Annotate | Download (13 KB)

1
/*
2
 * Copyright (C) 2007 Vitor Sessak <vitor1001@gmail.com>
3
 *
4
 * This file is part of Libav.
5
 *
6
 * Libav is free software; you can redistribute it and/or
7
 * modify it under the terms of the GNU Lesser General Public
8
 * License as published by the Free Software Foundation; either
9
 * version 2.1 of the License, or (at your option) any later version.
10
 *
11
 * Libav is distributed in the hope that it will be useful,
12
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
14
 * Lesser General Public License for more details.
15
 *
16
 * You should have received a copy of the GNU Lesser General Public
17
 * License along with Libav; if not, write to the Free Software
18
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19
 */
20

    
21
/**
22
 * @file
23
 * Codebook Generator using the ELBG algorithm
24
 */
25

    
26
#include <string.h>
27

    
28
#include "libavutil/lfg.h"
29
#include "elbg.h"
30
#include "avcodec.h"
31

    
32
#define DELTA_ERR_MAX 0.1  ///< Precision of the ELBG algorithm (as percentual error)
33

    
34
/**
35
 * In the ELBG jargon, a cell is the set of points that are closest to a
36
 * codebook entry. Not to be confused with a RoQ Video cell. */
37
typedef struct cell_s {
38
    int index;
39
    struct cell_s *next;
40
} cell;
41

    
42
/**
43
 * ELBG internal data
44
 */
45
typedef struct{
46
    int error;
47
    int dim;
48
    int numCB;
49
    int *codebook;
50
    cell **cells;
51
    int *utility;
52
    int *utility_inc;
53
    int *nearest_cb;
54
    int *points;
55
    AVLFG *rand_state;
56
    int *scratchbuf;
57
} elbg_data;
58

    
59
static inline int distance_limited(int *a, int *b, int dim, int limit)
60
{
61
    int i, dist=0;
62
    for (i=0; i<dim; i++) {
63
        dist += (a[i] - b[i])*(a[i] - b[i]);
64
        if (dist > limit)
65
            return INT_MAX;
66
    }
67

    
68
    return dist;
69
}
70

    
71
static inline void vect_division(int *res, int *vect, int div, int dim)
72
{
73
    int i;
74
    if (div > 1)
75
        for (i=0; i<dim; i++)
76
            res[i] = ROUNDED_DIV(vect[i],div);
77
    else if (res != vect)
78
        memcpy(res, vect, dim*sizeof(int));
79

    
80
}
81

    
82
static int eval_error_cell(elbg_data *elbg, int *centroid, cell *cells)
83
{
84
    int error=0;
85
    for (; cells; cells=cells->next)
86
        error += distance_limited(centroid, elbg->points + cells->index*elbg->dim, elbg->dim, INT_MAX);
87

    
88
    return error;
89
}
90

    
91
static int get_closest_codebook(elbg_data *elbg, int index)
92
{
93
    int i, pick=0, diff, diff_min = INT_MAX;
94
    for (i=0; i<elbg->numCB; i++)
95
        if (i != index) {
96
            diff = distance_limited(elbg->codebook + i*elbg->dim, elbg->codebook + index*elbg->dim, elbg->dim, diff_min);
97
            if (diff < diff_min) {
98
                pick = i;
99
                diff_min = diff;
100
            }
101
        }
102
    return pick;
103
}
104

    
105
static int get_high_utility_cell(elbg_data *elbg)
106
{
107
    int i=0;
108
    /* Using linear search, do binary if it ever turns to be speed critical */
109
    int r = av_lfg_get(elbg->rand_state)%elbg->utility_inc[elbg->numCB-1] + 1;
110
    while (elbg->utility_inc[i] < r)
111
        i++;
112

    
113
    assert(!elbg->cells[i]);
114

    
115
    return i;
116
}
117

    
118
/**
119
 * Implementation of the simple LBG algorithm for just two codebooks
120
 */
121
static int simple_lbg(elbg_data *elbg,
122
                      int dim,
123
                      int *centroid[3],
124
                      int newutility[3],
125
                      int *points,
126
                      cell *cells)
127
{
128
    int i, idx;
129
    int numpoints[2] = {0,0};
130
    int *newcentroid[2] = {
131
        elbg->scratchbuf + 3*dim,
132
        elbg->scratchbuf + 4*dim
133
    };
134
    cell *tempcell;
135

    
136
    memset(newcentroid[0], 0, 2 * dim * sizeof(*newcentroid[0]));
137

    
138
    newutility[0] =
139
    newutility[1] = 0;
140

    
141
    for (tempcell = cells; tempcell; tempcell=tempcell->next) {
142
        idx = distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX)>=
143
              distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX);
144
        numpoints[idx]++;
145
        for (i=0; i<dim; i++)
146
            newcentroid[idx][i] += points[tempcell->index*dim + i];
147
    }
148

    
149
    vect_division(centroid[0], newcentroid[0], numpoints[0], dim);
150
    vect_division(centroid[1], newcentroid[1], numpoints[1], dim);
151

    
152
    for (tempcell = cells; tempcell; tempcell=tempcell->next) {
153
        int dist[2] = {distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX),
154
                       distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX)};
155
        int idx = dist[0] > dist[1];
156
        newutility[idx] += dist[idx];
157
    }
158

    
159
    return newutility[0] + newutility[1];
160
}
161

    
162
static void get_new_centroids(elbg_data *elbg, int huc, int *newcentroid_i,
163
                              int *newcentroid_p)
164
{
165
    cell *tempcell;
166
    int *min = newcentroid_i;
167
    int *max = newcentroid_p;
168
    int i;
169

    
170
    for (i=0; i< elbg->dim; i++) {
171
        min[i]=INT_MAX;
172
        max[i]=0;
173
    }
174

    
175
    for (tempcell = elbg->cells[huc]; tempcell; tempcell = tempcell->next)
176
        for(i=0; i<elbg->dim; i++) {
177
            min[i]=FFMIN(min[i], elbg->points[tempcell->index*elbg->dim + i]);
178
            max[i]=FFMAX(max[i], elbg->points[tempcell->index*elbg->dim + i]);
179
        }
180

    
181
    for (i=0; i<elbg->dim; i++) {
182
        int ni = min[i] + (max[i] - min[i])/3;
183
        int np = min[i] + (2*(max[i] - min[i]))/3;
184
        newcentroid_i[i] = ni;
185
        newcentroid_p[i] = np;
186
    }
187
}
188

    
189
/**
190
 * Add the points in the low utility cell to its closest cell. Split the high
191
 * utility cell, putting the separed points in the (now empty) low utility
192
 * cell.
193
 *
194
 * @param elbg         Internal elbg data
195
 * @param indexes      {luc, huc, cluc}
196
 * @param newcentroid  A vector with the position of the new centroids
197
 */
198
static void shift_codebook(elbg_data *elbg, int *indexes,
199
                           int *newcentroid[3])
200
{
201
    cell *tempdata;
202
    cell **pp = &elbg->cells[indexes[2]];
203

    
204
    while(*pp)
205
        pp= &(*pp)->next;
206

    
207
    *pp = elbg->cells[indexes[0]];
208

    
209
    elbg->cells[indexes[0]] = NULL;
210
    tempdata = elbg->cells[indexes[1]];
211
    elbg->cells[indexes[1]] = NULL;
212

    
213
    while(tempdata) {
214
        cell *tempcell2 = tempdata->next;
215
        int idx = distance_limited(elbg->points + tempdata->index*elbg->dim,
216
                           newcentroid[0], elbg->dim, INT_MAX) >
217
                  distance_limited(elbg->points + tempdata->index*elbg->dim,
218
                           newcentroid[1], elbg->dim, INT_MAX);
219

    
220
        tempdata->next = elbg->cells[indexes[idx]];
221
        elbg->cells[indexes[idx]] = tempdata;
222
        tempdata = tempcell2;
223
    }
224
}
225

    
226
static void evaluate_utility_inc(elbg_data *elbg)
227
{
228
    int i, inc=0;
229

    
230
    for (i=0; i < elbg->numCB; i++) {
231
        if (elbg->numCB*elbg->utility[i] > elbg->error)
232
            inc += elbg->utility[i];
233
        elbg->utility_inc[i] = inc;
234
    }
235
}
236

    
237

    
238
static void update_utility_and_n_cb(elbg_data *elbg, int idx, int newutility)
239
{
240
    cell *tempcell;
241

    
242
    elbg->utility[idx] = newutility;
243
    for (tempcell=elbg->cells[idx]; tempcell; tempcell=tempcell->next)
244
        elbg->nearest_cb[tempcell->index] = idx;
245
}
246

    
247
/**
248
 * Evaluate if a shift lower the error. If it does, call shift_codebooks
249
 * and update elbg->error, elbg->utility and elbg->nearest_cb.
250
 *
251
 * @param elbg  Internal elbg data
252
 * @param idx   {luc (low utility cell, huc (high utility cell), cluc (closest cell to low utility cell)}
253
 */
254
static void try_shift_candidate(elbg_data *elbg, int idx[3])
255
{
256
    int j, k, olderror=0, newerror, cont=0;
257
    int newutility[3];
258
    int *newcentroid[3] = {
259
        elbg->scratchbuf,
260
        elbg->scratchbuf + elbg->dim,
261
        elbg->scratchbuf + 2*elbg->dim
262
    };
263
    cell *tempcell;
264

    
265
    for (j=0; j<3; j++)
266
        olderror += elbg->utility[idx[j]];
267

    
268
    memset(newcentroid[2], 0, elbg->dim*sizeof(int));
269

    
270
    for (k=0; k<2; k++)
271
        for (tempcell=elbg->cells[idx[2*k]]; tempcell; tempcell=tempcell->next) {
272
            cont++;
273
            for (j=0; j<elbg->dim; j++)
274
                newcentroid[2][j] += elbg->points[tempcell->index*elbg->dim + j];
275
        }
276

    
277
    vect_division(newcentroid[2], newcentroid[2], cont, elbg->dim);
278

    
279
    get_new_centroids(elbg, idx[1], newcentroid[0], newcentroid[1]);
280

    
281
    newutility[2]  = eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[0]]);
282
    newutility[2] += eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[2]]);
283

    
284
    newerror = newutility[2];
285

    
286
    newerror += simple_lbg(elbg, elbg->dim, newcentroid, newutility, elbg->points,
287
                           elbg->cells[idx[1]]);
288

    
289
    if (olderror > newerror) {
290
        shift_codebook(elbg, idx, newcentroid);
291

    
292
        elbg->error += newerror - olderror;
293

    
294
        for (j=0; j<3; j++)
295
            update_utility_and_n_cb(elbg, idx[j], newutility[j]);
296

    
297
        evaluate_utility_inc(elbg);
298
    }
299
 }
300

    
301
/**
302
 * Implementation of the ELBG block
303
 */
304
static void do_shiftings(elbg_data *elbg)
305
{
306
    int idx[3];
307

    
308
    evaluate_utility_inc(elbg);
309

    
310
    for (idx[0]=0; idx[0] < elbg->numCB; idx[0]++)
311
        if (elbg->numCB*elbg->utility[idx[0]] < elbg->error) {
312
            if (elbg->utility_inc[elbg->numCB-1] == 0)
313
                return;
314

    
315
            idx[1] = get_high_utility_cell(elbg);
316
            idx[2] = get_closest_codebook(elbg, idx[0]);
317

    
318
            if (idx[1] != idx[0] && idx[1] != idx[2])
319
                try_shift_candidate(elbg, idx);
320
        }
321
}
322

    
323
#define BIG_PRIME 433494437LL
324

    
325
void ff_init_elbg(int *points, int dim, int numpoints, int *codebook,
326
                  int numCB, int max_steps, int *closest_cb,
327
                  AVLFG *rand_state)
328
{
329
    int i, k;
330

    
331
    if (numpoints > 24*numCB) {
332
        /* ELBG is very costly for a big number of points. So if we have a lot
333
           of them, get a good initial codebook to save on iterations       */
334
        int *temp_points = av_malloc(dim*(numpoints/8)*sizeof(int));
335
        for (i=0; i<numpoints/8; i++) {
336
            k = (i*BIG_PRIME) % numpoints;
337
            memcpy(temp_points + i*dim, points + k*dim, dim*sizeof(int));
338
        }
339

    
340
        ff_init_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
341
        ff_do_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
342

    
343
        av_free(temp_points);
344

    
345
    } else  // If not, initialize the codebook with random positions
346
        for (i=0; i < numCB; i++)
347
            memcpy(codebook + i*dim, points + ((i*BIG_PRIME)%numpoints)*dim,
348
                   dim*sizeof(int));
349

    
350
}
351

    
352
void ff_do_elbg(int *points, int dim, int numpoints, int *codebook,
353
                int numCB, int max_steps, int *closest_cb,
354
                AVLFG *rand_state)
355
{
356
    int dist;
357
    elbg_data elbg_d;
358
    elbg_data *elbg = &elbg_d;
359
    int i, j, k, last_error, steps=0;
360
    int *dist_cb = av_malloc(numpoints*sizeof(int));
361
    int *size_part = av_malloc(numCB*sizeof(int));
362
    cell *list_buffer = av_malloc(numpoints*sizeof(cell));
363
    cell *free_cells;
364
    int best_dist, best_idx = 0;
365

    
366
    elbg->error = INT_MAX;
367
    elbg->dim = dim;
368
    elbg->numCB = numCB;
369
    elbg->codebook = codebook;
370
    elbg->cells = av_malloc(numCB*sizeof(cell *));
371
    elbg->utility = av_malloc(numCB*sizeof(int));
372
    elbg->nearest_cb = closest_cb;
373
    elbg->points = points;
374
    elbg->utility_inc = av_malloc(numCB*sizeof(int));
375
    elbg->scratchbuf = av_malloc(5*dim*sizeof(int));
376

    
377
    elbg->rand_state = rand_state;
378

    
379
    do {
380
        free_cells = list_buffer;
381
        last_error = elbg->error;
382
        steps++;
383
        memset(elbg->utility, 0, numCB*sizeof(int));
384
        memset(elbg->cells, 0, numCB*sizeof(cell *));
385

    
386
        elbg->error = 0;
387

    
388
        /* This loop evaluate the actual Voronoi partition. It is the most
389
           costly part of the algorithm. */
390
        for (i=0; i < numpoints; i++) {
391
            best_dist = distance_limited(elbg->points + i*elbg->dim, elbg->codebook + best_idx*elbg->dim, dim, INT_MAX);
392
            for (k=0; k < elbg->numCB; k++) {
393
                dist = distance_limited(elbg->points + i*elbg->dim, elbg->codebook + k*elbg->dim, dim, best_dist);
394
                if (dist < best_dist) {
395
                    best_dist = dist;
396
                    best_idx = k;
397
                }
398
            }
399
            elbg->nearest_cb[i] = best_idx;
400
            dist_cb[i] = best_dist;
401
            elbg->error += dist_cb[i];
402
            elbg->utility[elbg->nearest_cb[i]] += dist_cb[i];
403
            free_cells->index = i;
404
            free_cells->next = elbg->cells[elbg->nearest_cb[i]];
405
            elbg->cells[elbg->nearest_cb[i]] = free_cells;
406
            free_cells++;
407
        }
408

    
409
        do_shiftings(elbg);
410

    
411
        memset(size_part, 0, numCB*sizeof(int));
412

    
413
        memset(elbg->codebook, 0, elbg->numCB*dim*sizeof(int));
414

    
415
        for (i=0; i < numpoints; i++) {
416
            size_part[elbg->nearest_cb[i]]++;
417
            for (j=0; j < elbg->dim; j++)
418
                elbg->codebook[elbg->nearest_cb[i]*elbg->dim + j] +=
419
                    elbg->points[i*elbg->dim + j];
420
        }
421

    
422
        for (i=0; i < elbg->numCB; i++)
423
            vect_division(elbg->codebook + i*elbg->dim,
424
                          elbg->codebook + i*elbg->dim, size_part[i], elbg->dim);
425

    
426
    } while(((last_error - elbg->error) > DELTA_ERR_MAX*elbg->error) &&
427
            (steps < max_steps));
428

    
429
    av_free(dist_cb);
430
    av_free(size_part);
431
    av_free(elbg->utility);
432
    av_free(list_buffer);
433
    av_free(elbg->cells);
434
    av_free(elbg->utility_inc);
435
    av_free(elbg->scratchbuf);
436
}