libavcodec/elbg.c

   1 /*
   2  * Copyright (C) 2007 Vitor Sessak <vitor1001@gmail.com>
   3  *
   4  * This file is part of FFmpeg.
   5  *
   6  * FFmpeg 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  * FFmpeg 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 FFmpeg; 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 cbook_gen.c
  23  * Codebook Generator using the ELBG algorithm
  24  */
  25
  26 #include <string.h>
  27
  28 #include "libavutil/random.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     AVRandomState *rand_state;
  56 } elbg_data;
  57
  58 static inline int distance_limited(int *a, int *b, int dim, int limit)
  59 {
  60     int i, dist=0;
  61     for (i=0; i<dim; i++) {
  62         dist += (a[i] - b[i])*(a[i] - b[i]);
  63         if (dist > limit)
  64             return INT_MAX;
  65     }
  66
  67     return dist;
  68 }
  69
  70 static inline void vect_division(int *res, int *vect, int div, int dim)
  71 {
  72     int i;
  73     if (div > 1)
  74         for (i=0; i<dim; i++)
  75             res[i] = ROUNDED_DIV(vect[i],div);
  76     else if (res != vect)
  77         memcpy(res, vect, dim*sizeof(int));
  78
  79 }
  80
  81 static int eval_error_cell(elbg_data *elbg, int *centroid, cell *cells)
  82 {
  83     int error=0;
  84     for (; cells; cells=cells->next)
  85         error += distance_limited(centroid, elbg->points + cells->index*elbg->dim, elbg->dim, INT_MAX);
  86
  87     return error;
  88 }
  89
  90 static int get_closest_codebook(elbg_data *elbg, int index)
  91 {
  92     int i, pick=0, diff, diff_min = INT_MAX;
  93     for (i=0; i<elbg->numCB; i++)
  94         if (i != index) {
  95             diff = distance_limited(elbg->codebook + i*elbg->dim, elbg->codebook + index*elbg->dim, elbg->dim, diff_min);
  96             if (diff < diff_min) {
  97                 pick = i;
  98                 diff_min = diff;
  99             }
 100         }
 101     return pick;
 102 }
 103
 104 static int get_high_utility_cell(elbg_data *elbg)
 105 {
 106     int i=0;
 107     /* Using linear search, do binary if it ever turns to be speed critical */
 108     int r = av_random(elbg->rand_state)%elbg->utility_inc[elbg->numCB-1];
 109     while (elbg->utility_inc[i] < r)
 110         i++;
 111     return i;
 112 }
 113
 114 /**
 115  * Implementation of the simple LBG algorithm for just two codebooks
 116  */
 117 static int simple_lbg(int dim,
 118                       int *centroid[3],
 119                       int newutility[3],
 120                       int *points,
 121                       cell *cells)
 122 {
 123     int i, idx;
 124     int numpoints[2] = {0,0};
 125     int newcentroid[2][dim];
 126     cell *tempcell;
 127
 128     memset(newcentroid, 0, sizeof(newcentroid));
 129
 130     newutility[0] =
 131     newutility[1] = 0;
 132
 133     for (tempcell = cells; tempcell; tempcell=tempcell->next) {
 134         idx = distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX)>=
 135               distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX);
 136         numpoints[idx]++;
 137         for (i=0; i<dim; i++)
 138             newcentroid[idx][i] += points[tempcell->index*dim + i];
 139     }
 140
 141     vect_division(centroid[0], newcentroid[0], numpoints[0], dim);
 142     vect_division(centroid[1], newcentroid[1], numpoints[1], dim);
 143
 144     for (tempcell = cells; tempcell; tempcell=tempcell->next) {
 145         int dist[2] = {distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX),
 146                        distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX)};
 147         int idx = dist[0] > dist[1];
 148         newutility[idx] += dist[idx];
 149     }
 150
 151     return newutility[0] + newutility[1];
 152 }
 153
 154 static void get_new_centroids(elbg_data *elbg, int huc, int *newcentroid_i,
 155                               int *newcentroid_p)
 156 {
 157     cell *tempcell;
 158     int min[elbg->dim];
 159     int max[elbg->dim];
 160     int i;
 161
 162     for (i=0; i< elbg->dim; i++) {
 163         min[i]=INT_MAX;
 164         max[i]=0;
 165     }
 166
 167     for (tempcell = elbg->cells[huc]; tempcell; tempcell = tempcell->next)
 168         for(i=0; i<elbg->dim; i++) {
 169             min[i]=FFMIN(min[i], elbg->points[tempcell->index*elbg->dim + i]);
 170             max[i]=FFMAX(max[i], elbg->points[tempcell->index*elbg->dim + i]);
 171         }
 172
 173     for (i=0; i<elbg->dim; i++) {
 174         newcentroid_i[i] = min[i] + (max[i] - min[i])/3;
 175         newcentroid_p[i] = min[i] + (2*(max[i] - min[i]))/3;
 176     }
 177 }
 178
 179 /**
 180  * Add the points in the low utility cell to its closest cell. Split the high
 181  * utility cell, putting the separed points in the (now empty) low utility
 182  * cell.
 183  *
 184  * @param elbg         Internal elbg data
 185  * @param indexes      {luc, huc, cluc}
 186  * @param newcentroid  A vector with the position of the new centroids
 187  */
 188 static void shift_codebook(elbg_data *elbg, int *indexes,
 189                            int *newcentroid[3])
 190 {
 191     cell *tempdata;
 192     cell **pp = &elbg->cells[indexes[2]];
 193
 194     while(*pp)
 195         pp= &(*pp)->next;
 196
 197     *pp = elbg->cells[indexes[0]];
 198
 199     elbg->cells[indexes[0]] = NULL;
 200     tempdata = elbg->cells[indexes[1]];
 201     elbg->cells[indexes[1]] = NULL;
 202
 203     while(tempdata) {
 204         cell *tempcell2 = tempdata->next;
 205         int idx = distance_limited(elbg->points + tempdata->index*elbg->dim,
 206                            newcentroid[0], elbg->dim, INT_MAX) >
 207                   distance_limited(elbg->points + tempdata->index*elbg->dim,
 208                            newcentroid[1], elbg->dim, INT_MAX);
 209
 210         tempdata->next = elbg->cells[indexes[idx]];
 211         elbg->cells[indexes[idx]] = tempdata;
 212         tempdata = tempcell2;
 213     }
 214 }
 215
 216 static void evaluate_utility_inc(elbg_data *elbg)
 217 {
 218     int i, inc=0;
 219
 220     for (i=0; i < elbg->numCB; i++) {
 221         if (elbg->numCB*elbg->utility[i] > elbg->error)
 222             inc += elbg->utility[i];
 223         elbg->utility_inc[i] = inc;
 224     }
 225 }
 226
 227
 228 static void update_utility_and_n_cb(elbg_data *elbg, int idx, int newutility)
 229 {
 230     cell *tempcell;
 231
 232     elbg->utility[idx] = newutility;
 233     for (tempcell=elbg->cells[idx]; tempcell; tempcell=tempcell->next)
 234         elbg->nearest_cb[tempcell->index] = idx;
 235 }
 236
 237 /**
 238  * Evaluate if a shift lower the error. If it does, call shift_codebooks
 239  * and update elbg->error, elbg->utility and elbg->nearest_cb.
 240  *
 241  * @param elbg  Internal elbg data
 242  * @param indexes      {luc (low utility cell, huc (high utility cell), cluc (closest cell to low utility cell)}
 243  */
 244 static void try_shift_candidate(elbg_data *elbg, int idx[3])
 245 {
 246     int j, k, olderror=0, newerror, cont=0;
 247     int newutility[3];
 248     int newcentroid[3][elbg->dim];
 249     int *newcentroid_ptrs[3] = { newcentroid[0], newcentroid[1], newcentroid[2] };
 250     cell *tempcell;
 251
 252     for (j=0; j<3; j++)
 253         olderror += elbg->utility[idx[j]];
 254
 255     memset(newcentroid[2], 0, elbg->dim*sizeof(int));
 256
 257     for (k=0; k<2; k++)
 258         for (tempcell=elbg->cells[idx[2*k]]; tempcell; tempcell=tempcell->next) {
 259             cont++;
 260             for (j=0; j<elbg->dim; j++)
 261                 newcentroid[2][j] += elbg->points[tempcell->index*elbg->dim + j];
 262         }
 263
 264     vect_division(newcentroid[2], newcentroid[2], cont, elbg->dim);
 265
 266     get_new_centroids(elbg, idx[1], newcentroid[0], newcentroid[1]);
 267
 268     newutility[2]  = eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[0]]);
 269     newutility[2] += eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[2]]);
 270
 271     newerror = newutility[2];
 272
 273     newerror += simple_lbg(elbg->dim, newcentroid_ptrs, newutility, elbg->points,
 274                            elbg->cells[idx[1]]);
 275
 276     if (olderror > newerror) {
 277         shift_codebook(elbg, idx, newcentroid_ptrs);
 278
 279         elbg->error += newerror - olderror;
 280
 281         for (j=0; j<3; j++)
 282             update_utility_and_n_cb(elbg, idx[j], newutility[j]);
 283
 284         evaluate_utility_inc(elbg);
 285     }
 286  }
 287
 288 /**
 289  * Implementation of the ELBG block
 290  */
 291 static void do_shiftings(elbg_data *elbg)
 292 {
 293     int idx[3];
 294
 295     evaluate_utility_inc(elbg);
 296
 297     for (idx[0]=0; idx[0] < elbg->numCB; idx[0]++)
 298         if (elbg->numCB*elbg->utility[idx[0]] < elbg->error) {
 299             if (elbg->utility_inc[elbg->numCB-1] == 0)
 300                 return;
 301
 302             idx[1] = get_high_utility_cell(elbg);
 303             idx[2] = get_closest_codebook(elbg, idx[0]);
 304
 305             try_shift_candidate(elbg, idx);
 306         }
 307 }
 308
 309 #define BIG_PRIME 433494437LL
 310
 311 void ff_init_elbg(int *points, int dim, int numpoints, int *codebook,
 312                   int numCB, int max_steps, int *closest_cb,
 313                   AVRandomState *rand_state)
 314 {
 315     int i, k;
 316
 317     if (numpoints > 24*numCB) {
 318         /* ELBG is very costly for a big number of points. So if we have a lot
 319            of them, get a good initial codebook to save on iterations       */
 320         int *temp_points = av_malloc(dim*(numpoints/8)*sizeof(int));
 321         for (i=0; i<numpoints/8; i++) {
 322             k = (i*BIG_PRIME) % numpoints;
 323             memcpy(temp_points + i*dim, points + k*dim, dim*sizeof(int));
 324         }
 325
 326         ff_init_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
 327         ff_do_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
 328
 329         av_free(temp_points);
 330
 331     } else  // If not, initialize the codebook with random positions
 332         for (i=0; i < numCB; i++)
 333             memcpy(codebook + i*dim, points + ((i*BIG_PRIME)%numpoints)*dim,
 334                    dim*sizeof(int));
 335
 336 }
 337
 338 void ff_do_elbg(int *points, int dim, int numpoints, int *codebook,
 339                 int numCB, int max_steps, int *closest_cb,
 340                 AVRandomState *rand_state)
 341 {
 342     int dist;
 343     elbg_data elbg_d;
 344     elbg_data *elbg = &elbg_d;
 345     int i, j, k, last_error, steps=0;
 346     int *dist_cb = av_malloc(numpoints*sizeof(int));
 347     int *size_part = av_malloc(numCB*sizeof(int));
 348     cell *list_buffer = av_malloc(numpoints*sizeof(cell));
 349     cell *free_cells;
 350
 351     elbg->error = INT_MAX;
 352     elbg->dim = dim;
 353     elbg->numCB = numCB;
 354     elbg->codebook = codebook;
 355     elbg->cells = av_malloc(numCB*sizeof(cell *));
 356     elbg->utility = av_malloc(numCB*sizeof(int));
 357     elbg->nearest_cb = closest_cb;
 358     elbg->points = points;
 359     elbg->utility_inc = av_malloc(numCB*sizeof(int));
 360
 361     elbg->rand_state = rand_state;
 362
 363     do {
 364         free_cells = list_buffer;
 365         last_error = elbg->error;
 366         steps++;
 367         memset(elbg->utility, 0, numCB*sizeof(int));
 368         memset(elbg->cells, 0, numCB*sizeof(cell *));
 369
 370         elbg->error = 0;
 371
 372         /* This loop evaluate the actual Voronoi partition. It is the most
 373            costly part of the algorithm. */
 374         for (i=0; i < numpoints; i++) {
 375             dist_cb[i] = INT_MAX;
 376             for (k=0; k < elbg->numCB; k++) {
 377                 dist = distance_limited(elbg->points + i*elbg->dim, elbg->codebook + k*elbg->dim, dim, dist_cb[i]);
 378                 if (dist < dist_cb[i]) {
 379                     dist_cb[i] = dist;
 380                     elbg->nearest_cb[i] = k;
 381                 }
 382             }
 383             elbg->error += dist_cb[i];
 384             elbg->utility[elbg->nearest_cb[i]] += dist_cb[i];
 385             free_cells->index = i;
 386             free_cells->next = elbg->cells[elbg->nearest_cb[i]];
 387             elbg->cells[elbg->nearest_cb[i]] = free_cells;
 388             free_cells++;
 389         }
 390
 391         do_shiftings(elbg);
 392
 393         memset(size_part, 0, numCB*sizeof(int));
 394
 395         memset(elbg->codebook, 0, elbg->numCB*dim*sizeof(int));
 396
 397         for (i=0; i < numpoints; i++) {
 398             size_part[elbg->nearest_cb[i]]++;
 399             for (j=0; j < elbg->dim; j++)
 400                 elbg->codebook[elbg->nearest_cb[i]*elbg->dim + j] +=
 401                     elbg->points[i*elbg->dim + j];
 402         }
 403
 404         for (i=0; i < elbg->numCB; i++)
 405             vect_division(elbg->codebook + i*elbg->dim,
 406                           elbg->codebook + i*elbg->dim, size_part[i], elbg->dim);
 407
 408     } while(((last_error - elbg->error) > DELTA_ERR_MAX*elbg->error) &&
 409             (steps < max_steps));
 410
 411     av_free(dist_cb);
 412     av_free(size_part);
 413     av_free(elbg->utility);
 414     av_free(list_buffer);
 415     av_free(elbg->cells);
 416     av_free(elbg->utility_inc);
 417 }