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/*
Copyright (C) 2006 Pedro Felzenszwalb
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#ifndef SEGMENT_GRAPH
#define SEGMENT_GRAPH
#include <algorithm>
#include <cmath>
#include "disjoint-set.h"
// threshold function
#define THRESHOLD(size, c) (c/size)
typedef struct {
float w;
int a, b;
} edge;
bool operator<(const edge &a, const edge &b) {
return a.w < b.w;
}
/*
* Segment a graph
*
* Returns a disjoint-set forest representing the segmentation.
*
* num_vertices: number of vertices in graph.
* num_edges: number of edges in graph
* edges: array of edges.
* c: constant for treshold function.
*/
universe *segment_graph(int num_vertices, int num_edges, edge *edges,
float c) {
// sort edges by weight
std::sort(edges, edges + num_edges);
// make a disjoint-set forest
universe *u = new universe(num_vertices);
// init thresholds
float *threshold = new float[num_vertices];
for (int i = 0; i < num_vertices; i++)
threshold[i] = THRESHOLD(1,c);
// for each edge, in non-decreasing weight order...
for (int i = 0; i < num_edges; i++) {
edge *pedge = &edges[i];
// components conected by this edge
int a = u->find(pedge->a);
int b = u->find(pedge->b);
if (a != b) {
if ((pedge->w <= threshold[a]) &&
(pedge->w <= threshold[b])) {
u->join(a, b);
a = u->find(a);
threshold[a] = pedge->w + THRESHOLD(u->size(a), c);
}
}
}
// free up
delete threshold;
return u;
}
#endif
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