include/libstick/image.h

   1 #ifndef image_h_uiHiKahYooroomai
   2 #define image_h_uiHiKahYooroomai
   3
   4 #include "simplicialfunction.h"
   5
   6
   7 namespace libstick {
   8
   9 /** We consider an image, i.e. a rectangular arrangement of pixels, of given
  10  * height and width. Every pixel has a specific value (e.g., grey value) given
  11  * by the 'values' array as concatenation of all rows. We add every pixel as
  12  * vertex with its value as simplex value. We further triangulate the resulting
  13  * rectangular latice as a grid graph together with south-west to north-east
  14  * edges for each of the small squares of the grid graph. Finally the resulting
  15  * triangles are added. For all non-vertex simplices the maximum of its
  16  * vertex-values is used as its value. The first pixel is considered to be at
  17  * bottom-left.
  18  *
  19  * Requires that f.is_complete() gives true.
  20  * */
  21 template<class IT, class VT>
  22 void add_image_to_simplicialfunction(simplicial_function<2, IT, VT> &f, const VT *values, size_t width, size_t height) {
  23     assert(f.is_complete());
  24
  25     // Add the vertices
  26     const IT v1st = f.size();
  27     for (unsigned i=0; i < height; ++i)
  28         for (unsigned j=0; j < width; ++j)
  29             f.add_simplex(0, NULL, values[i*width + j]);
  30
  31     //      row i+1 o-------o
  32     //              |      /|
  33     //              |     / |
  34     //              |   2/  |
  35     //            0 |   /   |
  36     //              |  /    |
  37     //              | /     |
  38     //              |/  1   |
  39     //        row i o-------o
  40     //              ^
  41     //           column j
  42
  43     IT faces[3];
  44
  45     // Adding horizontal edges
  46     const IT he1st = f.size();
  47     for (unsigned i=0; i < height; ++i)
  48         for (unsigned j=0; j < width-1; ++j) {
  49             faces[0] = v1st + i*width + j;
  50             faces[1] = faces[0] + 1;
  51             f.add_simplex(1, faces);
  52         }
  53
  54     // Adding vertical edges
  55     const IT ve1st = f.size();
  56     for (unsigned i=0; i < height-1; ++i)
  57         for (unsigned j=0; j < width; ++j) {
  58             faces[0] = v1st + i*width + j;
  59             faces[1] = faces[0] + width;
  60             f.add_simplex(1, faces);
  61         }
  62
  63     // Adding diagonal edges
  64     const IT de1st = f.size();
  65     for (unsigned i=0; i < height-1; ++i)
  66         for (unsigned j=0; j < width-1; ++j) {
  67             faces[0] = v1st + i*width + j;
  68             faces[1] = faces[0] + width + 1;
  69             f.add_simplex(1, faces);
  70         }
  71
  72     // Add triangles
  73     for (unsigned i=0; i < height-1; ++i)
  74         for (unsigned j=0; j < width-1; ++j) {
  75             faces[0] = he1st + i*(width-1) + j;
  76             faces[1] = ve1st + i*width + j + 1;
  77             faces[2] = de1st + i*(width-1) + j;
  78             f.add_simplex(2, faces);
  79
  80             faces[0] = he1st + (i+1)*(width-1) + j;
  81             faces[1] = ve1st + i*width + j;
  82             faces[2] = de1st + i*(width-1) + j;
  83             f.add_simplex(2, faces);
  84         }
  85 }
  86
  87
  88 }
  89
  90 #endif
  91