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From: Jef Driesen (jefdriesen_at_[hidden])
Date: 2006-01-24 02:25:43

I'm trying to create a graph from an image, where pixel values are
regions labels. I have defined my graph to use lists instead of the
vectors (because I need to add/remove vertices and edges) and one extra
property for the vertex (the region label):

typedef boost::adjacency_list<
    boost::listS, // Adjacency list
    boost::listS, // Vertex list
    boost::undirectedS, // Undirected graph
    unsigned int, // Vertex property (=label)
    boost::no_property, // Edge property
    boost::no_property, // Graph property
    boost::listS // Edge list
> graph;
typedef boost::graph_traits<graph>::vertex_descriptor vertex_t;
typedef boost::graph_traits<graph>::edge_descriptor edge_t;

I have the following pseudo code to populate the graph:

graph g;
for each pixel (i,j) {
    unsigned int u_label = image[i][j];
    for each neighbourhood pixel (k,l) {
       unsigned int v_label = image[k][l];
       if (u_label != v_label) {
          // Find/add both vertices
          vertex_t u = boost::add_vertex(u_label,g);
          vertex_t v = boost::add_vertex(v_label, g);
          // Find/add edge
          boost::add_edge(u, v, g);

But this creates many duplicates (with regard to the label) for both
vertices and edges. How can i prevent this? Would using a set for the
edges solves my problem? And how can I add a vertex only if it does not
exist already?

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