libavcodec/elbg.c

   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/common.h"
  29 #include "libavutil/lfg.h"
  30 #include "elbg.h"
  31 #include "avcodec.h"
  32
  33 #define DELTA_ERR_MAX 0.1  ///< Precision of the ELBG algorithm (as percentual error)
  34
  35 /**
  36  * In the ELBG jargon, a cell is the set of points that are closest to a
  37  * codebook entry. Not to be confused with a RoQ Video cell. */
  38 typedef struct cell_s {
  39     int index;
  40     struct cell_s *next;
  41 } cell;
  42
  43 /**
  44  * ELBG internal data
  45  */
  46 typedef struct{
  47     int error;
  48     int dim;
  49     int numCB;
  50     int *codebook;
  51     cell **cells;
  52     int *utility;
  53     int *utility_inc;
  54     int *nearest_cb;
  55     int *points;
  56     AVLFG *rand_state;
  57     int *scratchbuf;
  58 } elbg_data;
  59
  60 static inline int distance_limited(int *a, int *b, int dim, int limit)
  61 {
  62     int i, dist=0;
  63     for (i=0; i<dim; i++) {
  64         dist += (a[i] - b[i])*(a[i] - b[i]);
  65         if (dist > limit)
  66             return INT_MAX;
  67     }
  68
  69     return dist;
  70 }
  71
  72 static inline void vect_division(int *res, int *vect, int div, int dim)
  73 {
  74     int i;
  75     if (div > 1)
  76         for (i=0; i<dim; i++)
  77             res[i] = ROUNDED_DIV(vect[i],div);
  78     else if (res != vect)
  79         memcpy(res, vect, dim*sizeof(int));
  80
  81 }
  82
  83 static int eval_error_cell(elbg_data *elbg, int *centroid, cell *cells)
  84 {
  85     int error=0;
  86     for (; cells; cells=cells->next)
  87         error += distance_limited(centroid, elbg->points + cells->index*elbg->dim, elbg->dim, INT_MAX);
  88
  89     return error;
  90 }
  91
  92 static int get_closest_codebook(elbg_data *elbg, int index)
  93 {
  94     int i, pick=0, diff, diff_min = INT_MAX;
  95     for (i=0; i<elbg->numCB; i++)
  96         if (i != index) {
  97             diff = distance_limited(elbg->codebook + i*elbg->dim, elbg->codebook + index*elbg->dim, elbg->dim, diff_min);
  98             if (diff < diff_min) {
  99                 pick = i;
 100                 diff_min = diff;
 101             }
 102         }
 103     return pick;
 104 }
 105
 106 static int get_high_utility_cell(elbg_data *elbg)
 107 {
 108     int i=0;
 109     /* Using linear search, do binary if it ever turns to be speed critical */
 110     int r = av_lfg_get(elbg->rand_state)%elbg->utility_inc[elbg->numCB-1] + 1;
 111     while (elbg->utility_inc[i] < r)
 112         i++;
 113
 114     assert(elbg->cells[i]);
 115
 116     return i;
 117 }
 118
 119 /**
 120  * Implementation of the simple LBG algorithm for just two codebooks
 121  */
 122 static int simple_lbg(elbg_data *elbg,
 123                       int dim,
 124                       int *centroid[3],
 125                       int newutility[3],
 126                       int *points,
 127                       cell *cells)
 128 {
 129     int i, idx;
 130     int numpoints[2] = {0,0};
 131     int *newcentroid[2] = {
 132         elbg->scratchbuf + 3*dim,
 133         elbg->scratchbuf + 4*dim
 134     };
 135     cell *tempcell;
 136
 137     memset(newcentroid[0], 0, 2 * dim * sizeof(*newcentroid[0]));
 138
 139     newutility[0] =
 140     newutility[1] = 0;
 141
 142     for (tempcell = cells; tempcell; tempcell=tempcell->next) {
 143         idx = distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX)>=
 144               distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX);
 145         numpoints[idx]++;
 146         for (i=0; i<dim; i++)
 147             newcentroid[idx][i] += points[tempcell->index*dim + i];
 148     }
 149
 150     vect_division(centroid[0], newcentroid[0], numpoints[0], dim);
 151     vect_division(centroid[1], newcentroid[1], numpoints[1], dim);
 152
 153     for (tempcell = cells; tempcell; tempcell=tempcell->next) {
 154         int dist[2] = {distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX),
 155                        distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX)};
 156         int idx = dist[0] > dist[1];
 157         newutility[idx] += dist[idx];
 158     }
 159
 160     return newutility[0] + newutility[1];
 161 }
 162
 163 static void get_new_centroids(elbg_data *elbg, int huc, int *newcentroid_i,
 164                               int *newcentroid_p)
 165 {
 166     cell *tempcell;
 167     int *min = newcentroid_i;
 168     int *max = newcentroid_p;
 169     int i;
 170
 171     for (i=0; i< elbg->dim; i++) {
 172         min[i]=INT_MAX;
 173         max[i]=0;
 174     }
 175
 176     for (tempcell = elbg->cells[huc]; tempcell; tempcell = tempcell->next)
 177         for(i=0; i<elbg->dim; i++) {
 178             min[i]=FFMIN(min[i], elbg->points[tempcell->index*elbg->dim + i]);
 179             max[i]=FFMAX(max[i], elbg->points[tempcell->index*elbg->dim + i]);
 180         }
 181
 182     for (i=0; i<elbg->dim; i++) {
 183         int ni = min[i] + (max[i] - min[i])/3;
 184         int np = min[i] + (2*(max[i] - min[i]))/3;
 185         newcentroid_i[i] = ni;
 186         newcentroid_p[i] = np;
 187     }
 188 }
 189
 190 /**
 191  * Add the points in the low utility cell to its closest cell. Split the high
 192  * utility cell, putting the separed points in the (now empty) low utility
 193  * cell.
 194  *
 195  * @param elbg         Internal elbg data
 196  * @param indexes      {luc, huc, cluc}
 197  * @param newcentroid  A vector with the position of the new centroids
 198  */
 199 static void shift_codebook(elbg_data *elbg, int *indexes,
 200                            int *newcentroid[3])
 201 {
 202     cell *tempdata;
 203     cell **pp = &elbg->cells[indexes[2]];
 204
 205     while(*pp)
 206         pp= &(*pp)->next;
 207
 208     *pp = elbg->cells[indexes[0]];
 209
 210     elbg->cells[indexes[0]] = NULL;
 211     tempdata = elbg->cells[indexes[1]];
 212     elbg->cells[indexes[1]] = NULL;
 213
 214     while(tempdata) {
 215         cell *tempcell2 = tempdata->next;
 216         int idx = distance_limited(elbg->points + tempdata->index*elbg->dim,
 217                            newcentroid[0], elbg->dim, INT_MAX) >
 218                   distance_limited(elbg->points + tempdata->index*elbg->dim,
 219                            newcentroid[1], elbg->dim, INT_MAX);
 220
 221         tempdata->next = elbg->cells[indexes[idx]];
 222         elbg->cells[indexes[idx]] = tempdata;
 223         tempdata = tempcell2;
 224     }
 225 }
 226
 227 static void evaluate_utility_inc(elbg_data *elbg)
 228 {
 229     int i, inc=0;
 230
 231     for (i=0; i < elbg->numCB; i++) {
 232         if (elbg->numCB*elbg->utility[i] > elbg->error)
 233             inc += elbg->utility[i];
 234         elbg->utility_inc[i] = inc;
 235     }
 236 }
 237
 238
 239 static void update_utility_and_n_cb(elbg_data *elbg, int idx, int newutility)
 240 {
 241     cell *tempcell;
 242
 243     elbg->utility[idx] = newutility;
 244     for (tempcell=elbg->cells[idx]; tempcell; tempcell=tempcell->next)
 245         elbg->nearest_cb[tempcell->index] = idx;
 246 }
 247
 248 /**
 249  * Evaluate if a shift lower the error. If it does, call shift_codebooks
 250  * and update elbg->error, elbg->utility and elbg->nearest_cb.
 251  *
 252  * @param elbg  Internal elbg data
 253  * @param idx   {luc (low utility cell, huc (high utility cell), cluc (closest cell to low utility cell)}
 254  */
 255 static void try_shift_candidate(elbg_data *elbg, int idx[3])
 256 {
 257     int j, k, olderror=0, newerror, cont=0;
 258     int newutility[3];
 259     int *newcentroid[3] = {
 260         elbg->scratchbuf,
 261         elbg->scratchbuf + elbg->dim,
 262         elbg->scratchbuf + 2*elbg->dim
 263     };
 264     cell *tempcell;
 265
 266     for (j=0; j<3; j++)
 267         olderror += elbg->utility[idx[j]];
 268
 269     memset(newcentroid[2], 0, elbg->dim*sizeof(int));
 270
 271     for (k=0; k<2; k++)
 272         for (tempcell=elbg->cells[idx[2*k]]; tempcell; tempcell=tempcell->next) {
 273             cont++;
 274             for (j=0; j<elbg->dim; j++)
 275                 newcentroid[2][j] += elbg->points[tempcell->index*elbg->dim + j];
 276         }
 277
 278     vect_division(newcentroid[2], newcentroid[2], cont, elbg->dim);
 279
 280     get_new_centroids(elbg, idx[1], newcentroid[0], newcentroid[1]);
 281
 282     newutility[2]  = eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[0]]);
 283     newutility[2] += eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[2]]);
 284
 285     newerror = newutility[2];
 286
 287     newerror += simple_lbg(elbg, elbg->dim, newcentroid, newutility, elbg->points,
 288                            elbg->cells[idx[1]]);
 289
 290     if (olderror > newerror) {
 291         shift_codebook(elbg, idx, newcentroid);
 292
 293         elbg->error += newerror - olderror;
 294
 295         for (j=0; j<3; j++)
 296             update_utility_and_n_cb(elbg, idx[j], newutility[j]);
 297
 298         evaluate_utility_inc(elbg);
 299     }
 300  }
 301
 302 /**
 303  * Implementation of the ELBG block
 304  */
 305 static void do_shiftings(elbg_data *elbg)
 306 {
 307     int idx[3];
 308
 309     evaluate_utility_inc(elbg);
 310
 311     for (idx[0]=0; idx[0] < elbg->numCB; idx[0]++)
 312         if (elbg->numCB*elbg->utility[idx[0]] < elbg->error) {
 313             if (elbg->utility_inc[elbg->numCB-1] == 0)
 314                 return;
 315
 316             idx[1] = get_high_utility_cell(elbg);
 317             idx[2] = get_closest_codebook(elbg, idx[0]);
 318
 319             if (idx[1] != idx[0] && idx[1] != idx[2])
 320                 try_shift_candidate(elbg, idx);
 321         }
 322 }
 323
 324 #define BIG_PRIME 433494437LL
 325
 326 void ff_init_elbg(int *points, int dim, int numpoints, int *codebook,
 327                   int numCB, int max_steps, int *closest_cb,
 328                   AVLFG *rand_state)
 329 {
 330     int i, k;
 331
 332     if (numpoints > 24*numCB) {
 333         /* ELBG is very costly for a big number of points. So if we have a lot
 334            of them, get a good initial codebook to save on iterations       */
 335         int *temp_points = av_malloc(dim*(numpoints/8)*sizeof(int));
 336         for (i=0; i<numpoints/8; i++) {
 337             k = (i*BIG_PRIME) % numpoints;
 338             memcpy(temp_points + i*dim, points + k*dim, dim*sizeof(int));
 339         }
 340
 341         ff_init_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
 342         ff_do_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
 343
 344         av_free(temp_points);
 345
 346     } else  // If not, initialize the codebook with random positions
 347         for (i=0; i < numCB; i++)
 348             memcpy(codebook + i*dim, points + ((i*BIG_PRIME)%numpoints)*dim,
 349                    dim*sizeof(int));
 350
 351 }
 352
 353 void ff_do_elbg(int *points, int dim, int numpoints, int *codebook,
 354                 int numCB, int max_steps, int *closest_cb,
 355                 AVLFG *rand_state)
 356 {
 357     int dist;
 358     elbg_data elbg_d;
 359     elbg_data *elbg = &elbg_d;
 360     int i, j, k, last_error, steps=0;
 361     int *dist_cb = av_malloc(numpoints*sizeof(int));
 362     int *size_part = av_malloc(numCB*sizeof(int));
 363     cell *list_buffer = av_malloc(numpoints*sizeof(cell));
 364     cell *free_cells;
 365     int best_dist, best_idx = 0;
 366
 367     elbg->error = INT_MAX;
 368     elbg->dim = dim;
 369     elbg->numCB = numCB;
 370     elbg->codebook = codebook;
 371     elbg->cells = av_malloc(numCB*sizeof(cell *));
 372     elbg->utility = av_malloc(numCB*sizeof(int));
 373     elbg->nearest_cb = closest_cb;
 374     elbg->points = points;
 375     elbg->utility_inc = av_malloc(numCB*sizeof(int));
 376     elbg->scratchbuf = av_malloc(5*dim*sizeof(int));
 377
 378     elbg->rand_state = rand_state;
 379
 380     do {
 381         free_cells = list_buffer;
 382         last_error = elbg->error;
 383         steps++;
 384         memset(elbg->utility, 0, numCB*sizeof(int));
 385         memset(elbg->cells, 0, numCB*sizeof(cell *));
 386
 387         elbg->error = 0;
 388
 389         /* This loop evaluate the actual Voronoi partition. It is the most
 390            costly part of the algorithm. */
 391         for (i=0; i < numpoints; i++) {
 392             best_dist = distance_limited(elbg->points + i*elbg->dim, elbg->codebook + best_idx*elbg->dim, dim, INT_MAX);
 393             for (k=0; k < elbg->numCB; k++) {
 394                 dist = distance_limited(elbg->points + i*elbg->dim, elbg->codebook + k*elbg->dim, dim, best_dist);
 395                 if (dist < best_dist) {
 396                     best_dist = dist;
 397                     best_idx = k;
 398                 }
 399             }
 400             elbg->nearest_cb[i] = best_idx;
 401             dist_cb[i] = best_dist;
 402             elbg->error += dist_cb[i];
 403             elbg->utility[elbg->nearest_cb[i]] += dist_cb[i];
 404             free_cells->index = i;
 405             free_cells->next = elbg->cells[elbg->nearest_cb[i]];
 406             elbg->cells[elbg->nearest_cb[i]] = free_cells;
 407             free_cells++;
 408         }
 409
 410         do_shiftings(elbg);
 411
 412         memset(size_part, 0, numCB*sizeof(int));
 413
 414         memset(elbg->codebook, 0, elbg->numCB*dim*sizeof(int));
 415
 416         for (i=0; i < numpoints; i++) {
 417             size_part[elbg->nearest_cb[i]]++;
 418             for (j=0; j < elbg->dim; j++)
 419                 elbg->codebook[elbg->nearest_cb[i]*elbg->dim + j] +=
 420                     elbg->points[i*elbg->dim + j];
 421         }
 422
 423         for (i=0; i < elbg->numCB; i++)
 424             vect_division(elbg->codebook + i*elbg->dim,
 425                           elbg->codebook + i*elbg->dim, size_part[i], elbg->dim);
 426
 427     } while(((last_error - elbg->error) > DELTA_ERR_MAX*elbg->error) &&
 428             (steps < max_steps));
 429
 430     av_free(dist_cb);
 431     av_free(size_part);
 432     av_free(elbg->utility);
 433     av_free(list_buffer);
 434     av_free(elbg->cells);
 435     av_free(elbg->utility_inc);
 436     av_free(elbg->scratchbuf);
 437 }