libavcodec/elbg.c
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00001 /*
00002  * Copyright (C) 2007 Vitor Sessak <vitor1001@gmail.com>
00003  *
00004  * This file is part of Libav.
00005  *
00006  * Libav is free software; you can redistribute it and/or
00007  * modify it under the terms of the GNU Lesser General Public
00008  * License as published by the Free Software Foundation; either
00009  * version 2.1 of the License, or (at your option) any later version.
00010  *
00011  * Libav is distributed in the hope that it will be useful,
00012  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00013  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014  * Lesser General Public License for more details.
00015  *
00016  * You should have received a copy of the GNU Lesser General Public
00017  * License along with Libav; if not, write to the Free Software
00018  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00019  */
00020 
00026 #include <string.h>
00027 
00028 #include "libavutil/lfg.h"
00029 #include "elbg.h"
00030 #include "avcodec.h"
00031 
00032 #define DELTA_ERR_MAX 0.1  ///< Precision of the ELBG algorithm (as percentual error)
00033 
00037 typedef struct cell_s {
00038     int index;
00039     struct cell_s *next;
00040 } cell;
00041 
00045 typedef struct{
00046     int error;
00047     int dim;
00048     int numCB;
00049     int *codebook;
00050     cell **cells;
00051     int *utility;
00052     int *utility_inc;
00053     int *nearest_cb;
00054     int *points;
00055     AVLFG *rand_state;
00056     int *scratchbuf;
00057 } elbg_data;
00058 
00059 static inline int distance_limited(int *a, int *b, int dim, int limit)
00060 {
00061     int i, dist=0;
00062     for (i=0; i<dim; i++) {
00063         dist += (a[i] - b[i])*(a[i] - b[i]);
00064         if (dist > limit)
00065             return INT_MAX;
00066     }
00067 
00068     return dist;
00069 }
00070 
00071 static inline void vect_division(int *res, int *vect, int div, int dim)
00072 {
00073     int i;
00074     if (div > 1)
00075         for (i=0; i<dim; i++)
00076             res[i] = ROUNDED_DIV(vect[i],div);
00077     else if (res != vect)
00078         memcpy(res, vect, dim*sizeof(int));
00079 
00080 }
00081 
00082 static int eval_error_cell(elbg_data *elbg, int *centroid, cell *cells)
00083 {
00084     int error=0;
00085     for (; cells; cells=cells->next)
00086         error += distance_limited(centroid, elbg->points + cells->index*elbg->dim, elbg->dim, INT_MAX);
00087 
00088     return error;
00089 }
00090 
00091 static int get_closest_codebook(elbg_data *elbg, int index)
00092 {
00093     int i, pick=0, diff, diff_min = INT_MAX;
00094     for (i=0; i<elbg->numCB; i++)
00095         if (i != index) {
00096             diff = distance_limited(elbg->codebook + i*elbg->dim, elbg->codebook + index*elbg->dim, elbg->dim, diff_min);
00097             if (diff < diff_min) {
00098                 pick = i;
00099                 diff_min = diff;
00100             }
00101         }
00102     return pick;
00103 }
00104 
00105 static int get_high_utility_cell(elbg_data *elbg)
00106 {
00107     int i=0;
00108     /* Using linear search, do binary if it ever turns to be speed critical */
00109     int r = av_lfg_get(elbg->rand_state)%elbg->utility_inc[elbg->numCB-1] + 1;
00110     while (elbg->utility_inc[i] < r)
00111         i++;
00112 
00113     assert(!elbg->cells[i]);
00114 
00115     return i;
00116 }
00117 
00121 static int simple_lbg(elbg_data *elbg,
00122                       int dim,
00123                       int *centroid[3],
00124                       int newutility[3],
00125                       int *points,
00126                       cell *cells)
00127 {
00128     int i, idx;
00129     int numpoints[2] = {0,0};
00130     int *newcentroid[2] = {
00131         elbg->scratchbuf + 3*dim,
00132         elbg->scratchbuf + 4*dim
00133     };
00134     cell *tempcell;
00135 
00136     memset(newcentroid[0], 0, 2 * dim * sizeof(*newcentroid[0]));
00137 
00138     newutility[0] =
00139     newutility[1] = 0;
00140 
00141     for (tempcell = cells; tempcell; tempcell=tempcell->next) {
00142         idx = distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX)>=
00143               distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX);
00144         numpoints[idx]++;
00145         for (i=0; i<dim; i++)
00146             newcentroid[idx][i] += points[tempcell->index*dim + i];
00147     }
00148 
00149     vect_division(centroid[0], newcentroid[0], numpoints[0], dim);
00150     vect_division(centroid[1], newcentroid[1], numpoints[1], dim);
00151 
00152     for (tempcell = cells; tempcell; tempcell=tempcell->next) {
00153         int dist[2] = {distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX),
00154                        distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX)};
00155         int idx = dist[0] > dist[1];
00156         newutility[idx] += dist[idx];
00157     }
00158 
00159     return newutility[0] + newutility[1];
00160 }
00161 
00162 static void get_new_centroids(elbg_data *elbg, int huc, int *newcentroid_i,
00163                               int *newcentroid_p)
00164 {
00165     cell *tempcell;
00166     int *min = newcentroid_i;
00167     int *max = newcentroid_p;
00168     int i;
00169 
00170     for (i=0; i< elbg->dim; i++) {
00171         min[i]=INT_MAX;
00172         max[i]=0;
00173     }
00174 
00175     for (tempcell = elbg->cells[huc]; tempcell; tempcell = tempcell->next)
00176         for(i=0; i<elbg->dim; i++) {
00177             min[i]=FFMIN(min[i], elbg->points[tempcell->index*elbg->dim + i]);
00178             max[i]=FFMAX(max[i], elbg->points[tempcell->index*elbg->dim + i]);
00179         }
00180 
00181     for (i=0; i<elbg->dim; i++) {
00182         int ni = min[i] + (max[i] - min[i])/3;
00183         int np = min[i] + (2*(max[i] - min[i]))/3;
00184         newcentroid_i[i] = ni;
00185         newcentroid_p[i] = np;
00186     }
00187 }
00188 
00198 static void shift_codebook(elbg_data *elbg, int *indexes,
00199                            int *newcentroid[3])
00200 {
00201     cell *tempdata;
00202     cell **pp = &elbg->cells[indexes[2]];
00203 
00204     while(*pp)
00205         pp= &(*pp)->next;
00206 
00207     *pp = elbg->cells[indexes[0]];
00208 
00209     elbg->cells[indexes[0]] = NULL;
00210     tempdata = elbg->cells[indexes[1]];
00211     elbg->cells[indexes[1]] = NULL;
00212 
00213     while(tempdata) {
00214         cell *tempcell2 = tempdata->next;
00215         int idx = distance_limited(elbg->points + tempdata->index*elbg->dim,
00216                            newcentroid[0], elbg->dim, INT_MAX) >
00217                   distance_limited(elbg->points + tempdata->index*elbg->dim,
00218                            newcentroid[1], elbg->dim, INT_MAX);
00219 
00220         tempdata->next = elbg->cells[indexes[idx]];
00221         elbg->cells[indexes[idx]] = tempdata;
00222         tempdata = tempcell2;
00223     }
00224 }
00225 
00226 static void evaluate_utility_inc(elbg_data *elbg)
00227 {
00228     int i, inc=0;
00229 
00230     for (i=0; i < elbg->numCB; i++) {
00231         if (elbg->numCB*elbg->utility[i] > elbg->error)
00232             inc += elbg->utility[i];
00233         elbg->utility_inc[i] = inc;
00234     }
00235 }
00236 
00237 
00238 static void update_utility_and_n_cb(elbg_data *elbg, int idx, int newutility)
00239 {
00240     cell *tempcell;
00241 
00242     elbg->utility[idx] = newutility;
00243     for (tempcell=elbg->cells[idx]; tempcell; tempcell=tempcell->next)
00244         elbg->nearest_cb[tempcell->index] = idx;
00245 }
00246 
00254 static void try_shift_candidate(elbg_data *elbg, int idx[3])
00255 {
00256     int j, k, olderror=0, newerror, cont=0;
00257     int newutility[3];
00258     int *newcentroid[3] = {
00259         elbg->scratchbuf,
00260         elbg->scratchbuf + elbg->dim,
00261         elbg->scratchbuf + 2*elbg->dim
00262     };
00263     cell *tempcell;
00264 
00265     for (j=0; j<3; j++)
00266         olderror += elbg->utility[idx[j]];
00267 
00268     memset(newcentroid[2], 0, elbg->dim*sizeof(int));
00269 
00270     for (k=0; k<2; k++)
00271         for (tempcell=elbg->cells[idx[2*k]]; tempcell; tempcell=tempcell->next) {
00272             cont++;
00273             for (j=0; j<elbg->dim; j++)
00274                 newcentroid[2][j] += elbg->points[tempcell->index*elbg->dim + j];
00275         }
00276 
00277     vect_division(newcentroid[2], newcentroid[2], cont, elbg->dim);
00278 
00279     get_new_centroids(elbg, idx[1], newcentroid[0], newcentroid[1]);
00280 
00281     newutility[2]  = eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[0]]);
00282     newutility[2] += eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[2]]);
00283 
00284     newerror = newutility[2];
00285 
00286     newerror += simple_lbg(elbg, elbg->dim, newcentroid, newutility, elbg->points,
00287                            elbg->cells[idx[1]]);
00288 
00289     if (olderror > newerror) {
00290         shift_codebook(elbg, idx, newcentroid);
00291 
00292         elbg->error += newerror - olderror;
00293 
00294         for (j=0; j<3; j++)
00295             update_utility_and_n_cb(elbg, idx[j], newutility[j]);
00296 
00297         evaluate_utility_inc(elbg);
00298     }
00299  }
00300 
00304 static void do_shiftings(elbg_data *elbg)
00305 {
00306     int idx[3];
00307 
00308     evaluate_utility_inc(elbg);
00309 
00310     for (idx[0]=0; idx[0] < elbg->numCB; idx[0]++)
00311         if (elbg->numCB*elbg->utility[idx[0]] < elbg->error) {
00312             if (elbg->utility_inc[elbg->numCB-1] == 0)
00313                 return;
00314 
00315             idx[1] = get_high_utility_cell(elbg);
00316             idx[2] = get_closest_codebook(elbg, idx[0]);
00317 
00318             if (idx[1] != idx[0] && idx[1] != idx[2])
00319                 try_shift_candidate(elbg, idx);
00320         }
00321 }
00322 
00323 #define BIG_PRIME 433494437LL
00324 
00325 void ff_init_elbg(int *points, int dim, int numpoints, int *codebook,
00326                   int numCB, int max_steps, int *closest_cb,
00327                   AVLFG *rand_state)
00328 {
00329     int i, k;
00330 
00331     if (numpoints > 24*numCB) {
00332         /* ELBG is very costly for a big number of points. So if we have a lot
00333            of them, get a good initial codebook to save on iterations       */
00334         int *temp_points = av_malloc(dim*(numpoints/8)*sizeof(int));
00335         for (i=0; i<numpoints/8; i++) {
00336             k = (i*BIG_PRIME) % numpoints;
00337             memcpy(temp_points + i*dim, points + k*dim, dim*sizeof(int));
00338         }
00339 
00340         ff_init_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
00341         ff_do_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
00342 
00343         av_free(temp_points);
00344 
00345     } else  // If not, initialize the codebook with random positions
00346         for (i=0; i < numCB; i++)
00347             memcpy(codebook + i*dim, points + ((i*BIG_PRIME)%numpoints)*dim,
00348                    dim*sizeof(int));
00349 
00350 }
00351 
00352 void ff_do_elbg(int *points, int dim, int numpoints, int *codebook,
00353                 int numCB, int max_steps, int *closest_cb,
00354                 AVLFG *rand_state)
00355 {
00356     int dist;
00357     elbg_data elbg_d;
00358     elbg_data *elbg = &elbg_d;
00359     int i, j, k, last_error, steps=0;
00360     int *dist_cb = av_malloc(numpoints*sizeof(int));
00361     int *size_part = av_malloc(numCB*sizeof(int));
00362     cell *list_buffer = av_malloc(numpoints*sizeof(cell));
00363     cell *free_cells;
00364     int best_dist, best_idx = 0;
00365 
00366     elbg->error = INT_MAX;
00367     elbg->dim = dim;
00368     elbg->numCB = numCB;
00369     elbg->codebook = codebook;
00370     elbg->cells = av_malloc(numCB*sizeof(cell *));
00371     elbg->utility = av_malloc(numCB*sizeof(int));
00372     elbg->nearest_cb = closest_cb;
00373     elbg->points = points;
00374     elbg->utility_inc = av_malloc(numCB*sizeof(int));
00375     elbg->scratchbuf = av_malloc(5*dim*sizeof(int));
00376 
00377     elbg->rand_state = rand_state;
00378 
00379     do {
00380         free_cells = list_buffer;
00381         last_error = elbg->error;
00382         steps++;
00383         memset(elbg->utility, 0, numCB*sizeof(int));
00384         memset(elbg->cells, 0, numCB*sizeof(cell *));
00385 
00386         elbg->error = 0;
00387 
00388         /* This loop evaluate the actual Voronoi partition. It is the most
00389            costly part of the algorithm. */
00390         for (i=0; i < numpoints; i++) {
00391             best_dist = distance_limited(elbg->points + i*elbg->dim, elbg->codebook + best_idx*elbg->dim, dim, INT_MAX);
00392             for (k=0; k < elbg->numCB; k++) {
00393                 dist = distance_limited(elbg->points + i*elbg->dim, elbg->codebook + k*elbg->dim, dim, best_dist);
00394                 if (dist < best_dist) {
00395                     best_dist = dist;
00396                     best_idx = k;
00397                 }
00398             }
00399             elbg->nearest_cb[i] = best_idx;
00400             dist_cb[i] = best_dist;
00401             elbg->error += dist_cb[i];
00402             elbg->utility[elbg->nearest_cb[i]] += dist_cb[i];
00403             free_cells->index = i;
00404             free_cells->next = elbg->cells[elbg->nearest_cb[i]];
00405             elbg->cells[elbg->nearest_cb[i]] = free_cells;
00406             free_cells++;
00407         }
00408 
00409         do_shiftings(elbg);
00410 
00411         memset(size_part, 0, numCB*sizeof(int));
00412 
00413         memset(elbg->codebook, 0, elbg->numCB*dim*sizeof(int));
00414 
00415         for (i=0; i < numpoints; i++) {
00416             size_part[elbg->nearest_cb[i]]++;
00417             for (j=0; j < elbg->dim; j++)
00418                 elbg->codebook[elbg->nearest_cb[i]*elbg->dim + j] +=
00419                     elbg->points[i*elbg->dim + j];
00420         }
00421 
00422         for (i=0; i < elbg->numCB; i++)
00423             vect_division(elbg->codebook + i*elbg->dim,
00424                           elbg->codebook + i*elbg->dim, size_part[i], elbg->dim);
00425 
00426     } while(((last_error - elbg->error) > DELTA_ERR_MAX*elbg->error) &&
00427             (steps < max_steps));
00428 
00429     av_free(dist_cb);
00430     av_free(size_part);
00431     av_free(elbg->utility);
00432     av_free(list_buffer);
00433     av_free(elbg->cells);
00434     av_free(elbg->utility_inc);
00435     av_free(elbg->scratchbuf);
00436 }