Codebook generator using the ELBG algorithm

patch by Vitor: printf(vitor%d gmail com, 1001)
original thread: Re: [FFmpeg-devel] [PATCH] Add a codebook generator
                 (was: [PATCH] RoQ video encoder, take 2)
date: 05/28/2007 01:21 PM

Originally committed as revision 9196 to svn://svn.ffmpeg.org/ffmpeg/trunk

Changelog

@@ -86,6 +86,7 @@ version <next>
 - Renderware TXD demuxer and decoder
 - extern C declarations for C++ removed from headers
 - sws_flags command line option
+- codebook generator
 
 version 0.4.9-pre1:
 

libavcodec/elbg.c

@@ -0,0 +1,416 @@
+/*
+ * Copyright (C) 2007 Vitor <vitor1001@gmail.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file cbook_gen.c
+ * Codebook Generator using the ELBG algorithm
+ */
+
+#include <string.h>
+
+#include "elbg.h"
+#include "avcodec.h"
+#include "random.h"
+
+#define DELTA_ERR_MAX 0.1  ///< Precision of the ELBG algorithm (as percentual error)
+
+/**
+ * In the ELBG jargon, a cell is the set of points that are closest to a
+ * codebook entry. Not to be confused with a RoQ Video cell. */
+typedef struct cell_s {
+    int index;
+    struct cell_s *next;
+} cell;
+
+/**
+ * ELBG internal data
+ */
+typedef struct{
+    int error;
+    int dim;
+    int numCB;
+    int *codebook;
+    cell **cells;
+    int *utility;
+    int *utility_inc;
+    int *nearest_cb;
+    int *points;
+    AVRandomState *rand_state;
+} elbg_data;
+
+static inline int distance_limited(int *a, int *b, int dim, int limit)
+{
+    int i, dist=0;
+    for (i=0; i<dim; i++) {
+        dist += (a[i] - b[i])*(a[i] - b[i]);
+        if (dist > limit)
+            return INT_MAX;
+    }
+
+    return dist;
+}
+
+static inline void vect_division(int *res, int *vect, int div, int dim)
+{
+    int i;
+    if (div > 1)
+        for (i=0; i<dim; i++)
+            res[i] = ROUNDED_DIV(vect[i],div);
+    else if (res != vect)
+        memcpy(res, vect, dim*sizeof(int));
+
+}
+
+static int eval_error_cell(elbg_data *elbg, int *centroid, cell *cells)
+{
+    int error=0;
+    for (; cells; cells=cells->next)
+        error += distance_limited(centroid, elbg->points + cells->index*elbg->dim, elbg->dim, INT_MAX);
+
+    return error;
+}
+
+static int get_closest_codebook(elbg_data *elbg, int index)
+{
+    int i, pick=0, diff, diff_min = INT_MAX;
+    for (i=0; i<elbg->numCB; i++)
+        if (i != index) {
+            diff = distance_limited(elbg->codebook + i*elbg->dim, elbg->codebook + index*elbg->dim, elbg->dim, diff_min);
+            if (diff < diff_min) {
+                pick = i;
+                diff_min = diff;
+            }
+        }
+    return pick;
+}
+
+static int get_high_utility_cell(elbg_data *elbg)
+{
+    int i=0;
+    /* Using linear search, do binary if it ever turns to be speed critical */
+    int r = av_random(elbg->rand_state)%elbg->utility_inc[elbg->numCB-1];
+    while (elbg->utility_inc[i] < r)
+        i++;
+    return i;
+}
+
+/**
+ * Implementation of the simple LBG algorithm for just two codebooks
+ */
+static int simple_lbg(int dim,
+                      int centroid[3][dim],
+                      int newutility[3],
+                      int *points,
+                      cell *cells)
+{
+    int i, idx;
+    int numpoints[2] = {0,0};
+    int newcentroid[2][dim];
+    cell *tempcell;
+
+    memset(newcentroid, 0, sizeof(newcentroid));
+
+    newutility[0] =
+    newutility[1] = 0;
+
+    for (tempcell = cells; tempcell; tempcell=tempcell->next) {
+        idx = distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX)>=
+              distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX);
+        numpoints[idx]++;
+        for (i=0; i<dim; i++)
+            newcentroid[idx][i] += points[tempcell->index*dim + i];
+    }
+
+    vect_division(centroid[0], newcentroid[0], numpoints[0], dim);
+    vect_division(centroid[1], newcentroid[1], numpoints[1], dim);
+
+    for (tempcell = cells; tempcell; tempcell=tempcell->next) {
+        int dist[2] = {distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX),
+                       distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX)};
+        int idx = dist[0] > dist[1];
+        newutility[idx] += dist[idx];
+    }
+
+    return newutility[0] + newutility[1];
+}
+
+static void get_new_centroids(elbg_data *elbg, int huc, int *newcentroid_i,
+                              int *newcentroid_p)
+{
+    cell *tempcell;
+    int min[elbg->dim];
+    int max[elbg->dim];
+    int i;
+
+    for (i=0; i< elbg->dim; i++) {
+        min[i]=INT_MAX;
+        max[i]=0;
+    }
+
+    for (tempcell = elbg->cells[huc]; tempcell; tempcell = tempcell->next)
+        for(i=0; i<elbg->dim; i++) {
+            min[i]=FFMIN(min[i], elbg->points[tempcell->index*elbg->dim + i]);
+            max[i]=FFMAX(max[i], elbg->points[tempcell->index*elbg->dim + i]);
+        }
+
+    for (i=0; i<elbg->dim; i++) {
+        newcentroid_i[i] = min[i] + (max[i] - min[i])/3;
+        newcentroid_p[i] = min[i] + (2*(max[i] - min[i]))/3;
+    }
+}
+
+/**
+ * Add the points in the low utility cell to its closest cell. Split the high
+ * utility cell, putting the separed points in the (now empty) low utility
+ * cell.
+ *
+ * @param elbg         Internal elbg data
+ * @param indexes      {luc, huc, cluc}
+ * @param newcentroid  A vector with the position of the new centroids
+ */
+static void shift_codebook(elbg_data *elbg, int *indexes,
+                           int newcentroid[3][elbg->dim])
+{
+    cell *tempdata;
+    cell **pp = &elbg->cells[indexes[2]];
+
+    while(*pp)
+        pp= &(*pp)->next;
+
+    *pp = elbg->cells[indexes[0]];
+
+    elbg->cells[indexes[0]] = NULL;
+    tempdata = elbg->cells[indexes[1]];
+    elbg->cells[indexes[1]] = NULL;
+
+    while(tempdata) {
+        cell *tempcell2 = tempdata->next;
+        int idx = distance_limited(elbg->points + tempdata->index*elbg->dim,
+                           newcentroid[0], elbg->dim, INT_MAX) >
+                  distance_limited(elbg->points + tempdata->index*elbg->dim,
+                           newcentroid[1], elbg->dim, INT_MAX);
+
+        tempdata->next = elbg->cells[indexes[idx]];
+        elbg->cells[indexes[idx]] = tempdata;
+        tempdata = tempcell2;
+    }
+}
+
+static void evaluate_utility_inc(elbg_data *elbg)
+{
+    int i, inc=0;
+
+    for (i=0; i < elbg->numCB; i++) {
+        if (elbg->numCB*elbg->utility[i] > elbg->error)
+            inc += elbg->utility[i];
+        elbg->utility_inc[i] = inc;
+    }
+}
+
+
+static void update_utility_and_n_cb(elbg_data *elbg, int idx, int newutility)
+{
+    cell *tempcell;
+
+    elbg->utility[idx] = newutility;
+    for (tempcell=elbg->cells[idx]; tempcell; tempcell=tempcell->next)
+        elbg->nearest_cb[tempcell->index] = idx;
+}
+
+/**
+ * Evaluate if a shift lower the error. If it does, call shift_codebooks
+ * and update elbg->error, elbg->utility and elbg->nearest_cb.
+ *
+ * @param elbg  Internal elbg data
+ * @param indexes      {luc (low utility cell, huc (high utility cell), cluc (closest cell to low utility cell)}
+ */
+static void try_shift_candidate(elbg_data *elbg, int idx[3])
+{
+    int j, k, olderror=0, newerror, cont=0;
+    int newutility[3];
+    int newcentroid[3][elbg->dim];
+    cell *tempcell;
+
+    for (j=0; j<3; j++)
+        olderror += elbg->utility[idx[j]];
+
+    memset(newcentroid[2], 0, elbg->dim*sizeof(int));
+
+    for (k=0; k<2; k++)
+        for (tempcell=elbg->cells[idx[2*k]]; tempcell; tempcell=tempcell->next) {
+            cont++;
+            for (j=0; j<elbg->dim; j++)
+                newcentroid[2][j] += elbg->points[tempcell->index*elbg->dim + j];
+        }
+
+    vect_division(newcentroid[2], newcentroid[2], cont, elbg->dim);
+
+    get_new_centroids(elbg, idx[1], newcentroid[0], newcentroid[1]);
+
+    newutility[2]  = eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[0]]);
+    newutility[2] += eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[2]]);
+
+    newerror = newutility[2];
+
+    newerror += simple_lbg(elbg->dim, newcentroid, newutility, elbg->points,
+                           elbg->cells[idx[1]]);
+
+    if (olderror > newerror) {
+        shift_codebook(elbg, idx, newcentroid);
+
+        elbg->error += newerror - olderror;
+
+        for (j=0; j<3; j++)
+            update_utility_and_n_cb(elbg, idx[j], newutility[j]);
+
+        evaluate_utility_inc(elbg);
+    }
+ }
+
+/**
+ * Implementation of the ELBG block
+ */
+static void do_shiftings(elbg_data *elbg)
+{
+    int idx[3];
+
+    evaluate_utility_inc(elbg);
+
+    for (idx[0]=0; idx[0] < elbg->numCB; idx[0]++)
+        if (elbg->numCB*elbg->utility[idx[0]] < elbg->error) {
+            if (elbg->utility_inc[elbg->numCB-1] == 0)
+                return;
+
+            idx[1] = get_high_utility_cell(elbg);
+            idx[2] = get_closest_codebook(elbg, idx[0]);
+
+            try_shift_candidate(elbg, idx);
+        }
+}
+
+#define BIG_PRIME 433494437LL
+
+void ff_init_elbg(int *points, int dim, int numpoints, int *codebook,
+                  int numCB, int max_steps, int *closest_cb,
+                  AVRandomState *rand_state)
+{
+    int i, k;
+
+    if (numpoints > 24*numCB) {
+        /* ELBG is very costly for a big number of points. So if we have a lot
+           of them, get a good initial codebook to save on iterations       */
+        int *temp_points = av_malloc(dim*(numpoints/8)*sizeof(int));
+        for (i=0; i<numpoints/8; i++) {
+            k = (i*BIG_PRIME) % numpoints;
+            memcpy(temp_points + i*dim, points + k*dim, dim*sizeof(int));
+        }
+
+        ff_init_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
+        ff_do_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
+
+        av_free(temp_points);
+
+    } else  // If not, initialize the codebook with random positions
+        for (i=0; i < numCB; i++)
+            memcpy(codebook + i*dim, points + ((i*BIG_PRIME)%numpoints)*dim,
+                   dim*sizeof(int));
+
+}
+
+void ff_do_elbg(int *points, int dim, int numpoints, int *codebook,
+                int numCB, int max_steps, int *closest_cb,
+                AVRandomState *rand_state)
+{
+    int dist;
+    elbg_data elbg_d;
+    elbg_data *elbg = &elbg_d;
+    int i, j, k, last_error, steps=0;
+    int *dist_cb = av_malloc(numpoints*sizeof(int));
+    int *size_part = av_malloc(numCB*sizeof(int));
+    cell *list_buffer = av_malloc(numpoints*sizeof(cell));
+    cell *free_cells;
+
+    elbg->error = INT_MAX;
+    elbg->dim = dim;
+    elbg->numCB = numCB;
+    elbg->codebook = codebook;
+    elbg->cells = av_malloc(numCB*sizeof(cell *));
+    elbg->utility = av_malloc(numCB*sizeof(int));
+    elbg->nearest_cb = closest_cb;
+    elbg->points = points;
+    elbg->utility_inc = av_malloc(numCB*sizeof(int));
+
+    elbg->rand_state = rand_state;
+
+    do {
+        free_cells = list_buffer;
+        last_error = elbg->error;
+        steps++;
+        memset(elbg->utility, 0, numCB*sizeof(int));
+        memset(elbg->cells, 0, numCB*sizeof(cell *));
+
+        elbg->error = 0;
+
+        /* This loop evaluate the actual Voronoi partition. It is the most
+           costly part of the algorithm. */
+        for (i=0; i < numpoints; i++) {
+            dist_cb[i] = INT_MAX;
+            for (k=0; k < elbg->numCB; k++) {
+                dist = distance_limited(elbg->points + i*elbg->dim, elbg->codebook + k*elbg->dim, dim, dist_cb[i]);
+                if (dist < dist_cb[i]) {
+                    dist_cb[i] = dist;
+                    elbg->nearest_cb[i] = k;
+                }
+            }
+            elbg->error += dist_cb[i];
+            elbg->utility[elbg->nearest_cb[i]] += dist_cb[i];
+            free_cells->index = i;
+            free_cells->next = elbg->cells[elbg->nearest_cb[i]];
+            elbg->cells[elbg->nearest_cb[i]] = free_cells;
+            free_cells++;
+        }
+
+        do_shiftings(elbg);
+
+        memset(size_part, 0, numCB*sizeof(int));
+
+        memset(elbg->codebook, 0, elbg->numCB*dim*sizeof(int));
+
+        for (i=0; i < numpoints; i++) {
+            size_part[elbg->nearest_cb[i]]++;
+            for (j=0; j < elbg->dim; j++)
+                elbg->codebook[elbg->nearest_cb[i]*elbg->dim + j] +=
+                    elbg->points[i*elbg->dim + j];
+        }
+
+        for (i=0; i < elbg->numCB; i++)
+            vect_division(elbg->codebook + i*elbg->dim,
+                          elbg->codebook + i*elbg->dim, size_part[i], elbg->dim);
+
+    } while(((last_error - elbg->error) > DELTA_ERR_MAX*elbg->error) &&
+            (steps < max_steps));
+
+    av_free(dist_cb);
+    av_free(size_part);
+    av_free(elbg->utility);
+    av_free(list_buffer);
+    av_free(elbg->cells);
+    av_free(elbg->utility_inc);
+}

libavcodec/elbg.h

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2007 Vitor <vitor1001@gmail.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "random.h"
+
+/**
+ * Implementation of the Enhanced LBG Algorithm
+ * Based on the paper "Neural Networks 14:1219-1237" that can be found in
+ * http://citeseer.ist.psu.edu/patan01enhanced.html .
+ *
+ * @param points Input points.
+ * @param dim Dimension of the points.
+ * @param numpoints Num of points in **points.
+ * @param codebook Pointer to the output codebook. Must be allocated.
+ * @param numCB Number of points in the codebook.
+ * @param num_steps The maximum number of steps. One step is already a good compromise between time and quality.
+ * @param closest_cb Return the closest codebook to each point. Must be allocated.
+ * @param rand_state A random number generator state. Should be already initialised by av_init_random.
+ */
+void ff_do_elbg(int *points, int dim, int numpoints, int *codebook,
+                int numCB, int num_steps, int *closest_cb,
+                AVRandomState *rand_state);
+
+/**
+ * Initialize the **codebook vector for the elbg algorithm. If you have already
+ * a codebook and you want to refine it, you shouldn't call this function.
+ * If numpoints < 8*numCB this function fills **codebook with random numbers.
+ * If not, it calls ff_do_elbg for a (smaller) random sample of the points in
+ * **points. Get the same parameters as ff_do_elbg.
+ */
+void ff_init_elbg(int *points, int dim, int numpoints, int *codebook,
+                  int numCB, int num_steps, int *closest_cb,
+                  AVRandomState *rand_state);