Added another overload of find_max_factor_graph_potts() that works on

graphs that are regular grids.

dlib/graph_cuts/find_max_factor_graph_potts.h

@@ -9,6 +9,7 @@
 #include "general_potts_problem.h"
 #include "../algs.h"
 #include "../graph_utils.h"
+#include "../array2d.h"
 
 namespace dlib
 {
@@ -410,6 +411,139 @@ namespace dlib
             }
 
         };
+
+// ----------------------------------------------------------------------------------------
+
+        template <
+            typename label_image_type,
+            typename image_potts_model
+            >
+        class potts_grid_problem 
+        {
+            label_image_type& label_img;
+            long nc;
+            long num_nodes;
+            unsigned char* labels;
+            const image_potts_model& model;
+
+        public:
+            const static unsigned long max_number_of_neighbors = 4;
+
+            potts_grid_problem (
+                label_image_type& label_img_,
+                const image_potts_model& image_potts_model_
+            ) : 
+                label_img(label_img_),
+                model(image_potts_model_)
+            {
+                num_nodes = model.nr()*model.nc();
+                nc = model.nc();
+                labels = &label_img[0][0];
+            }
+
+            unsigned long number_of_nodes (
+            ) const { return num_nodes; }
+
+            unsigned long number_of_neighbors (
+                unsigned long 
+            ) const 
+            { 
+                return 4;
+            }
+
+            unsigned long get_neighbor_idx (
+                long node_id1,
+                long node_id2
+            ) const
+            {
+                long diff = node_id2-node_id1;
+                if (diff > nc)
+                    diff -= (long)number_of_nodes();
+                else if (diff < -nc)
+                    diff += (long)number_of_nodes();
+
+                if (diff == 1) 
+                    return 0;
+                else if (diff == -1)
+                    return 1;
+                else if (diff == nc)
+                    return 2;
+                else
+                    return 3;
+            }
+
+            unsigned long get_neighbor (
+                long node_id,
+                long idx
+            ) const
+            {
+                switch(idx)
+                {
+                    case 0: 
+                        {
+                            long temp = node_id+1;
+                            if (temp < (long)number_of_nodes())
+                                return temp;
+                            else
+                                return temp - (long)number_of_nodes();
+                        }
+                    case 1: 
+                        {
+                            long temp = node_id-1;
+                            if (node_id >= 1)
+                                return temp;
+                            else
+                                return temp + (long)number_of_nodes();
+                        }
+                    case 2: 
+                        {
+                            long temp = node_id+nc;
+                            if (temp < (long)number_of_nodes())
+                                return temp;
+                            else
+                                return temp - (long)number_of_nodes();
+                        }
+                    case 3: 
+                        {
+                            long temp = node_id-nc;
+                            if (node_id >= nc)
+                                return temp;
+                            else
+                                return temp + (long)number_of_nodes();
+                        }
+                }
+                return 0;
+            }
+
+            void set_label (
+                const unsigned long& idx,
+                node_label value
+            )
+            {
+                *(labels+idx) = value;
+            }
+
+            node_label get_label (
+                const unsigned long& idx
+            ) const
+            {
+                return *(labels+idx);
+            }
+
+            typedef typename image_potts_model::value_type value_type;
+
+            value_type factor_value (unsigned long idx) const
+            {
+                return model.factor_value(idx);
+            }
+
+            value_type factor_value_disagreement (unsigned long idx1, unsigned long idx2) const
+            {
+                return model.factor_value_disagreement(idx1,idx2);
+            }
+
+        };
+
     }
 
 // ----------------------------------------------------------------------------------------
@@ -531,6 +665,29 @@ namespace dlib
         return score;
     }
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename potts_grid_problem,
+        typename mem_manager
+        >
+    typename potts_grid_problem::value_type potts_model_score (
+        const potts_grid_problem& prob,
+        const array2d<node_label,mem_manager>& labels
+    )
+    {
+        DLIB_ASSERT(prob.nr() == labels.nr() && prob.nc() == labels.nc(),
+            "\t value_type potts_model_score(prob,labels)"
+            << "\n\t Invalid inputs were given to this function." 
+            << "\n\t prob.nr(): " << labels.nr()
+            << "\n\t prob.nc(): " << labels.nc()
+            );
+        typedef array2d<node_label,mem_manager> image_type;
+        // This const_cast is ok because the model object won't actually modify labels
+        dlib::impl::potts_grid_problem<image_type,potts_grid_problem> model(const_cast<image_type&>(labels),prob);
+        return potts_model_score(model);
+    }
+
 // ----------------------------------------------------------------------------------------
 
     template <
@@ -640,6 +797,23 @@ namespace dlib
 
     }
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename potts_grid_problem,
+        typename mem_manager
+        >
+    void find_max_factor_graph_potts (
+        const potts_grid_problem& prob,
+        array2d<node_label,mem_manager>& labels
+    )
+    {
+        typedef array2d<node_label,mem_manager> image_type;
+        labels.set_size(prob.nr(), prob.nc());
+        dlib::impl::potts_grid_problem<image_type,potts_grid_problem> model(labels,prob);
+        find_max_factor_graph_potts(model);
+    }
+
 // ---------------------------------------------------------------------------------------- 
 
 }

dlib/graph_cuts/find_max_factor_graph_potts_abstract.h

@@ -6,6 +6,7 @@
 #include "../matrix.h"
 #include "min_cut_abstract.h"
 #include "../graph_utils.h"
+#include "../array2d/array2d_kernel_abstract.h"
 
 namespace dlib
 {
@@ -159,6 +160,83 @@ namespace dlib
 
     };
 
+// ----------------------------------------------------------------------------------------
+
+    struct potts_grid_problem 
+    {
+        /*!
+            WHAT THIS OBJECT REPRESENTS
+                This object is a specialization of a potts_problem to the case where
+                the graph is a regular grid where each node is connected to its four
+                neighbors.  An example of this is an image where each pixel is a node
+                and is connected to its four immediate neighboring pixels.  Therefore,
+                this object defines the interface this special kind of MAP problem
+                must implement if it is to be solved by the find_max_factor_graph_potts(potts_grid_problem,array2d)
+                routine defined at the end of this file.
+
+
+                Note that all nodes always have four neighbors, even nodes on the edge
+                of the graph.  This is because these border nodes are connected to
+                the border nodes on the other side of the graph.  That is, the graph
+                "wraps" around at the borders.  
+        !*/
+
+        // This typedef should be for a type like int or double.  It
+        // must also be capable of representing signed values.
+        typedef an_integer_or_real_type value_type;
+
+        long nr(
+        ) const; 
+        /*!
+            ensures
+                - returns the number of rows in the grid
+        !*/
+
+        long nc(
+        ) const;
+        /*!
+            ensures
+                - returns the number of columns in the grid
+        !*/
+
+        value_type factor_value (
+            unsigned long idx
+        ) const;
+        /*!
+            requires
+                - idx < nr()*nc()
+            ensures
+                - The grid is represented in row-major-order format.  Therefore, idx
+                  identifies a node according to its position in the row-major-order 
+                  representation of the grid graph.  Or in other words, idx corresponds
+                  to the following row and column location:
+                    - row == idx/nc()
+                    - col == idx%nc()
+                - returns a value which indicates how "good" it is to assign the idx-th 
+                  node the label of true.  The larger the value, the more desirable it is 
+                  to give it this label.  Similarly, a negative value indicates that it is
+                  better to give the node a label of false.
+        !*/
+
+        value_type factor_value_disagreement (
+            unsigned long idx1,
+            unsigned long idx2
+        ) const;
+        /*!
+            requires
+                - idx1 < nr()*nc()
+                - idx2 < nr()*nc()
+                - idx1 != idx2
+                - the idx1-th node and idx2-th node are neighbors in the grid graph.  
+            ensures
+                - returns a number >= 0.  This is the penalty for giving node idx1 and idx2
+                  different labels.  Larger values indicate a larger penalty.
+                - this function is symmetric.  That is, it is true that: 
+                  factor_value_disagreement(i,j) == factor_value_disagreement(j,i)
+        !*/
+    };
+
+// ----------------------------------------------------------------------------------------
 // ----------------------------------------------------------------------------------------
 
     template <
@@ -230,6 +308,44 @@ namespace dlib
                 - Then this function returns F - D
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename potts_grid_problem,
+        typename mem_manager
+        >
+    typename potts_grid_problem::value_type potts_model_score (
+        const potts_grid_problem& prob,
+        const array2d<node_label,mem_manager>& labels
+    );
+    /*!
+        requires
+            - prob.nr() == labels.nr()
+            - prob.nc() == labels.nc()
+            - potts_grid_problem == an object with an interface compatible with the 
+              potts_grid_problem object defined above.
+            - for all valid i and j:
+                - prob.factor_value_disagreement(i,j) >= 0
+                - prob.factor_value_disagreement(i,j) == prob.factor_value_disagreement(j,i)
+        ensures
+            - computes the model score for the given potts_grid_problem.  We define this
+              precisely below:
+                - let L(i) == the boolean label of the i-th variable in prob.  Or in other 
+                  words, L(i) == (labels[i/labels.nc()][i%labels.nc()] != 0).
+                - let F == the sum of values of prob.factor_value(i) for only i values
+                  where L(i) == true.
+                - Let D == the sum of values of prob.factor_value_disagreement(i,j) 
+                  for only i and j values which meet the following conditions:
+                    - i and j are neighbors in the graph defined by prob, that is,
+                      it is valid to call prob.factor_value_disagreement(i,j).
+                    - L(i) != L(j)
+                    - i < j
+                      (i.e. We want to make sure to only count the edge between i and j once)
+
+                - Then this function returns F - D
+    !*/
+
+// ----------------------------------------------------------------------------------------
 // ----------------------------------------------------------------------------------------
 
     template <
@@ -283,6 +399,33 @@ namespace dlib
                 - the factor_value_disagreement(i,j) is stored in edge(g,i,j).
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename potts_grid_problem,
+        typename mem_manager
+        >
+    void find_max_factor_graph_potts (
+        const potts_grid_problem& prob,
+        array2d<node_label,mem_manager>& labels
+    );
+    /*!
+        requires
+            - potts_grid_problem == an object with an interface compatible with the 
+              potts_grid_problem object defined above.
+            - for all valid i and j:
+                - prob.factor_value_disagreement(i,j) >= 0
+                - prob.factor_value_disagreement(i,j) == prob.factor_value_disagreement(j,i)
+        ensures
+            - This routine solves a version of a potts problem where the graph is a
+              regular grid where each node is connected to its four immediate neighbors.
+              In particular, this means that this function finds the assignments 
+              to all the labels in prob which maximizes potts_model_score(prob,#labels).
+            - The optimal labels are stored in #labels.
+            - #labels.nr() == prob.nr()
+            - #labels.nc() == prob.nc()
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
 }