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 libavcodec/elbg.c
  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 } 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_lfg_get(elbg->rand_state)%elbg->utility_inc[elbg->numCB-1] + 1;
 109     while (elbg->utility_inc[i] < r)
 110         i++;
 111
 112     assert(!elbg->cells[i]);
 113
 114     return i;
 115 }
 116
 117 /**
 118  * Implementation of the simple LBG algorithm for just two codebooks
 119  */
 120 static int simple_lbg(int dim,
 121                       int *centroid[3],
 122                       int newutility[3],
 123                       int *points,
 124                       cell *cells)
 125 {
 126     int i, idx;
 127     int numpoints[2] = {0,0};
 128     int newcentroid[2][dim];
 129     cell *tempcell;
 130
 131     memset(newcentroid, 0, sizeof(newcentroid));
 132
 133     newutility[0] =
 134     newutility[1] = 0;
 135
 136     for (tempcell = cells; tempcell; tempcell=tempcell->next) {
 137         idx = distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX)>=
 138               distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX);
 139         numpoints[idx]++;
 140         for (i=0; i<dim; i++)
 141             newcentroid[idx][i] += points[tempcell->index*dim + i];
 142     }
 143
 144     vect_division(centroid[0], newcentroid[0], numpoints[0], dim);
 145     vect_division(centroid[1], newcentroid[1], numpoints[1], dim);
 146
 147     for (tempcell = cells; tempcell; tempcell=tempcell->next) {
 148         int dist[2] = {distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX),
 149                        distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX)};
 150         int idx = dist[0] > dist[1];
 151         newutility[idx] += dist[idx];
 152     }
 153
 154     return newutility[0] + newutility[1];
 155 }
 156
 157 static void get_new_centroids(elbg_data *elbg, int huc, int *newcentroid_i,
 158                               int *newcentroid_p)
 159 {
 160     cell *tempcell;
 161     int min[elbg->dim];
 162     int max[elbg->dim];
 163     int i;
 164
 165     for (i=0; i< elbg->dim; i++) {
 166         min[i]=INT_MAX;
 167         max[i]=0;
 168     }
 169
 170     for (tempcell = elbg->cells[huc]; tempcell; tempcell = tempcell->next)
 171         for(i=0; i<elbg->dim; i++) {
 172             min[i]=FFMIN(min[i], elbg->points[tempcell->index*elbg->dim + i]);
 173             max[i]=FFMAX(max[i], elbg->points[tempcell->index*elbg->dim + i]);
 174         }
 175
 176     for (i=0; i<elbg->dim; i++) {
 177         newcentroid_i[i] = min[i] + (max[i] - min[i])/3;
 178         newcentroid_p[i] = min[i] + (2*(max[i] - min[i]))/3;
 179     }
 180 }
 181
 182 /**
 183  * Add the points in the low utility cell to its closest cell. Split the high
 184  * utility cell, putting the separed points in the (now empty) low utility
 185  * cell.
 186  *
 187  * @param elbg         Internal elbg data
 188  * @param indexes      {luc, huc, cluc}
 189  * @param newcentroid  A vector with the position of the new centroids
 190  */
 191 static void shift_codebook(elbg_data *elbg, int *indexes,
 192                            int *newcentroid[3])
 193 {
 194     cell *tempdata;
 195     cell **pp = &elbg->cells[indexes[2]];
 196
 197     while(*pp)
 198         pp= &(*pp)->next;
 199
 200     *pp = elbg->cells[indexes[0]];
 201
 202     elbg->cells[indexes[0]] = NULL;
 203     tempdata = elbg->cells[indexes[1]];
 204     elbg->cells[indexes[1]] = NULL;
 205
 206     while(tempdata) {
 207         cell *tempcell2 = tempdata->next;
 208         int idx = distance_limited(elbg->points + tempdata->index*elbg->dim,
 209                            newcentroid[0], elbg->dim, INT_MAX) >
 210                   distance_limited(elbg->points + tempdata->index*elbg->dim,
 211                            newcentroid[1], elbg->dim, INT_MAX);
 212
 213         tempdata->next = elbg->cells[indexes[idx]];
 214         elbg->cells[indexes[idx]] = tempdata;
 215         tempdata = tempcell2;
 216     }
 217 }
 218
 219 static void evaluate_utility_inc(elbg_data *elbg)
 220 {
 221     int i, inc=0;
 222
 223     for (i=0; i < elbg->numCB; i++) {
 224         if (elbg->numCB*elbg->utility[i] > elbg->error)
 225             inc += elbg->utility[i];
 226         elbg->utility_inc[i] = inc;
 227     }
 228 }
 229
 230
 231 static void update_utility_and_n_cb(elbg_data *elbg, int idx, int newutility)
 232 {
 233     cell *tempcell;
 234
 235     elbg->utility[idx] = newutility;
 236     for (tempcell=elbg->cells[idx]; tempcell; tempcell=tempcell->next)
 237         elbg->nearest_cb[tempcell->index] = idx;
 238 }
 239
 240 /**
 241  * Evaluate if a shift lower the error. If it does, call shift_codebooks
 242  * and update elbg->error, elbg->utility and elbg->nearest_cb.
 243  *
 244  * @param elbg  Internal elbg data
 245  * @param indexes      {luc (low utility cell, huc (high utility cell), cluc (closest cell to low utility cell)}
 246  */
 247 static void try_shift_candidate(elbg_data *elbg, int idx[3])
 248 {
 249     int j, k, olderror=0, newerror, cont=0;
 250     int newutility[3];
 251     int newcentroid[3][elbg->dim];
 252     int *newcentroid_ptrs[3];
 253     cell *tempcell;
 254
 255     newcentroid_ptrs[0] = newcentroid[0];
 256     newcentroid_ptrs[1] = newcentroid[1];
 257     newcentroid_ptrs[2] = newcentroid[2];
 258
 259     for (j=0; j<3; j++)
 260         olderror += elbg->utility[idx[j]];
 261
 262     memset(newcentroid[2], 0, elbg->dim*sizeof(int));
 263
 264     for (k=0; k<2; k++)
 265         for (tempcell=elbg->cells[idx[2*k]]; tempcell; tempcell=tempcell->next) {
 266             cont++;
 267             for (j=0; j<elbg->dim; j++)
 268                 newcentroid[2][j] += elbg->points[tempcell->index*elbg->dim + j];
 269         }
 270
 271     vect_division(newcentroid[2], newcentroid[2], cont, elbg->dim);
 272
 273     get_new_centroids(elbg, idx[1], newcentroid[0], newcentroid[1]);
 274
 275     newutility[2]  = eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[0]]);
 276     newutility[2] += eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[2]]);
 277
 278     newerror = newutility[2];
 279
 280     newerror += simple_lbg(elbg->dim, newcentroid_ptrs, newutility, elbg->points,
 281                            elbg->cells[idx[1]]);
 282
 283     if (olderror > newerror) {
 284         shift_codebook(elbg, idx, newcentroid_ptrs);
 285
 286         elbg->error += newerror - olderror;
 287
 288         for (j=0; j<3; j++)
 289             update_utility_and_n_cb(elbg, idx[j], newutility[j]);
 290
 291         evaluate_utility_inc(elbg);
 292     }
 293  }
 294
 295 /**
 296  * Implementation of the ELBG block
 297  */
 298 static void do_shiftings(elbg_data *elbg)
 299 {
 300     int idx[3];
 301
 302     evaluate_utility_inc(elbg);
 303
 304     for (idx[0]=0; idx[0] < elbg->numCB; idx[0]++)
 305         if (elbg->numCB*elbg->utility[idx[0]] < elbg->error) {
 306             if (elbg->utility_inc[elbg->numCB-1] == 0)
 307                 return;
 308
 309             idx[1] = get_high_utility_cell(elbg);
 310             idx[2] = get_closest_codebook(elbg, idx[0]);
 311
 312             if (idx[1] != idx[0] && idx[1] != idx[2])
 313                 try_shift_candidate(elbg, idx);
 314         }
 315 }
 316
 317 #define BIG_PRIME 433494437LL
 318
 319 void ff_init_elbg(int *points, int dim, int numpoints, int *codebook,
 320                   int numCB, int max_steps, int *closest_cb,
 321                   AVLFG *rand_state)
 322 {
 323     int i, k;
 324
 325     if (numpoints > 24*numCB) {
 326         /* ELBG is very costly for a big number of points. So if we have a lot
 327            of them, get a good initial codebook to save on iterations       */
 328         int *temp_points = av_malloc(dim*(numpoints/8)*sizeof(int));
 329         for (i=0; i<numpoints/8; i++) {
 330             k = (i*BIG_PRIME) % numpoints;
 331             memcpy(temp_points + i*dim, points + k*dim, dim*sizeof(int));
 332         }
 333
 334         ff_init_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
 335         ff_do_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
 336
 337         av_free(temp_points);
 338
 339     } else  // If not, initialize the codebook with random positions
 340         for (i=0; i < numCB; i++)
 341             memcpy(codebook + i*dim, points + ((i*BIG_PRIME)%numpoints)*dim,
 342                    dim*sizeof(int));
 343
 344 }
 345
 346 void ff_do_elbg(int *points, int dim, int numpoints, int *codebook,
 347                 int numCB, int max_steps, int *closest_cb,
 348                 AVLFG *rand_state)
 349 {
 350     int dist;
 351     elbg_data elbg_d;
 352     elbg_data *elbg = &elbg_d;
 353     int i, j, k, last_error, steps=0;
 354     int *dist_cb = av_malloc(numpoints*sizeof(int));
 355     int *size_part = av_malloc(numCB*sizeof(int));
 356     cell *list_buffer = av_malloc(numpoints*sizeof(cell));
 357     cell *free_cells;
 358
 359     elbg->error = INT_MAX;
 360     elbg->dim = dim;
 361     elbg->numCB = numCB;
 362     elbg->codebook = codebook;
 363     elbg->cells = av_malloc(numCB*sizeof(cell *));
 364     elbg->utility = av_malloc(numCB*sizeof(int));
 365     elbg->nearest_cb = closest_cb;
 366     elbg->points = points;
 367     elbg->utility_inc = av_malloc(numCB*sizeof(int));
 368
 369     elbg->rand_state = rand_state;
 370
 371     do {
 372         free_cells = list_buffer;
 373         last_error = elbg->error;
 374         steps++;
 375         memset(elbg->utility, 0, numCB*sizeof(int));
 376         memset(elbg->cells, 0, numCB*sizeof(cell *));
 377
 378         elbg->error = 0;
 379
 380         /* This loop evaluate the actual Voronoi partition. It is the most
 381            costly part of the algorithm. */
 382         for (i=0; i < numpoints; i++) {
 383             dist_cb[i] = INT_MAX;
 384             for (k=0; k < elbg->numCB; k++) {
 385                 dist = distance_limited(elbg->points + i*elbg->dim, elbg->codebook + k*elbg->dim, dim, dist_cb[i]);
 386                 if (dist < dist_cb[i]) {
 387                     dist_cb[i] = dist;
 388                     elbg->nearest_cb[i] = k;
 389                 }
 390             }
 391             elbg->error += dist_cb[i];
 392             elbg->utility[elbg->nearest_cb[i]] += dist_cb[i];
 393             free_cells->index = i;
 394             free_cells->next = elbg->cells[elbg->nearest_cb[i]];
 395             elbg->cells[elbg->nearest_cb[i]] = free_cells;
 396             free_cells++;
 397         }
 398
 399         do_shiftings(elbg);
 400
 401         memset(size_part, 0, numCB*sizeof(int));
 402
 403         memset(elbg->codebook, 0, elbg->numCB*dim*sizeof(int));
 404
 405         for (i=0; i < numpoints; i++) {
 406             size_part[elbg->nearest_cb[i]]++;
 407             for (j=0; j < elbg->dim; j++)
 408                 elbg->codebook[elbg->nearest_cb[i]*elbg->dim + j] +=
 409                     elbg->points[i*elbg->dim + j];
 410         }
 411
 412         for (i=0; i < elbg->numCB; i++)
 413             vect_division(elbg->codebook + i*elbg->dim,
 414                           elbg->codebook + i*elbg->dim, size_part[i], elbg->dim);
 415
 416     } while(((last_error - elbg->error) > DELTA_ERR_MAX*elbg->error) &&
 417             (steps < max_steps));
 418
 419     av_free(dist_cb);
 420     av_free(size_part);
 421     av_free(elbg->utility);
 422     av_free(list_buffer);
 423     av_free(elbg->cells);
 424     av_free(elbg->utility_inc);
 425 }