Merge pull request #2765 from pradeep-pyro:kullback_leibler

modules/imgproc/doc/histograms.rst

@@ -181,6 +181,8 @@ Compares two histograms.
 
             * **CV_COMP_HELLINGER**     Synonym for ``CV_COMP_BHATTACHARYYA``
 
+            * **CV_COMP_KL_DIV**     Kullback-Leibler divergence
+
 The functions ``compareHist`` compare two dense or two sparse histograms using the specified method:
 
 * Correlation (``method=CV_COMP_CORREL``)
@@ -224,6 +226,12 @@ The functions ``compareHist`` compare two dense or two sparse histograms using t
 
         d(H_1,H_2) =  \sqrt{1 - \frac{1}{\sqrt{\bar{H_1} \bar{H_2} N^2}} \sum_I \sqrt{H_1(I) \cdot H_2(I)}}
 
+* Kullback-Leibler divergence (``method=CV_COMP_KL_DIV``).
+
+    .. math::
+
+        d(H_1,H_2) = \sum _I H_1(I) \log \left(\frac{H_1(I)}{H_2(I)}\right)
+
 The function returns
 :math:`d(H_1, H_2)` .
 

modules/imgproc/include/opencv2/imgproc.hpp

@@ -204,7 +204,8 @@ enum { HISTCMP_CORREL        = 0,
        HISTCMP_INTERSECT     = 2,
        HISTCMP_BHATTACHARYYA = 3,
        HISTCMP_HELLINGER     = HISTCMP_BHATTACHARYYA,
-       HISTCMP_CHISQR_ALT    = 4
+       HISTCMP_CHISQR_ALT    = 4,
+       HISTCMP_KL_DIV        = 5
      };
 
 //! the color conversion code

modules/imgproc/include/opencv2/imgproc/types_c.h

@@ -509,7 +509,8 @@ enum
     CV_COMP_INTERSECT     =2,
     CV_COMP_BHATTACHARYYA =3,
     CV_COMP_HELLINGER     =CV_COMP_BHATTACHARYYA,
-    CV_COMP_CHISQR_ALT    =4
+    CV_COMP_CHISQR_ALT    =4,
+    CV_COMP_KL_DIV        =5
 };
 
 /* Mask size for distance transform */

modules/imgproc/src/histogram.cpp

@@ -2325,6 +2325,21 @@ double cv::compareHist( InputArray _H1, InputArray _H2, int method )
                 s2 += b;
             }
         }
+        else if( method == CV_COMP_KL_DIV )
+        {
+            for( j = 0; j < len; j++ )
+            {
+                double p = h1[j];
+                double q = h2[j];
+                if( fabs(p) <= DBL_EPSILON ) {
+                    continue;
+                }
+                if(  fabs(q) <= DBL_EPSILON ) {
+                    q = 1e-10;
+                }
+                result += p * std::log( p / q );
+            }
+        }
         else
             CV_Error( CV_StsBadArg, "Unknown comparison method" );
     }
@@ -2360,7 +2375,7 @@ double cv::compareHist( const SparseMat& H1, const SparseMat& H2, int method )
         CV_Assert( H1.size(i) == H2.size(i) );
 
     const SparseMat *PH1 = &H1, *PH2 = &H2;
-    if( PH1->nzcount() > PH2->nzcount() && method != CV_COMP_CHISQR && method != CV_COMP_CHISQR_ALT)
+    if( PH1->nzcount() > PH2->nzcount() && method != CV_COMP_CHISQR && method != CV_COMP_CHISQR_ALT && method != CV_COMP_KL_DIV )
         std::swap(PH1, PH2);
 
     SparseMatConstIterator it = PH1->begin();
@@ -2440,6 +2455,18 @@ double cv::compareHist( const SparseMat& H1, const SparseMat& H2, int method )
         s1 = fabs(s1) > FLT_EPSILON ? 1./std::sqrt(s1) : 1.;
         result = std::sqrt(std::max(1. - result*s1, 0.));
     }
+    else if( method == CV_COMP_KL_DIV )
+    {
+        for( i = 0; i < N1; i++, ++it )
+        {
+            double v1 = it.value<float>();
+            const SparseMat::Node* node = it.node();
+            double v2 = PH2->value<float>(node->idx, (size_t*)&node->hashval);
+            if( !v2 )
+                v2 = 1e-10;
+            result += v1 * std::log( v1 / v2 );
+        }
+    }
     else
         CV_Error( CV_StsBadArg, "Unknown comparison method" );
 
@@ -2785,7 +2812,7 @@ cvCompareHist( const CvHistogram* hist1,
     CvSparseMatIterator iterator;
     CvSparseNode *node1, *node2;
 
-    if( mat1->heap->active_count > mat2->heap->active_count && method != CV_COMP_CHISQR && method != CV_COMP_CHISQR_ALT)
+    if( mat1->heap->active_count > mat2->heap->active_count && method != CV_COMP_CHISQR && method != CV_COMP_CHISQR_ALT && method != CV_COMP_KL_DIV )
     {
         CvSparseMat* t;
         CV_SWAP( mat1, mat2, t );
@@ -2887,6 +2914,13 @@ cvCompareHist( const CvHistogram* hist1,
         result = 1. - result*s1;
         result = sqrt(MAX(result,0.));
     }
+    else if( method == CV_COMP_KL_DIV )
+    {
+        cv::SparseMat sH1, sH2;
+        ((const CvSparseMat*)hist1->bins)->copyToSparseMat(sH1);
+        ((const CvSparseMat*)hist2->bins)->copyToSparseMat(sH2);
+        result = cv::compareHist( sH1, sH2, CV_COMP_KL_DIV );
+    }
     else
         CV_Error( CV_StsBadArg, "Unknown comparison method" );
 

modules/imgproc/test/test_histograms.cpp

@@ -948,7 +948,7 @@ int CV_ThreshHistTest::validate_test_results( int /*test_case_idx*/ )
 class CV_CompareHistTest : public CV_BaseHistTest
 {
 public:
-    enum { MAX_METHOD = 5 };
+    enum { MAX_METHOD = 6 };
 
     CV_CompareHistTest();
 protected:
@@ -1021,6 +1021,13 @@ int CV_CompareHistTest::validate_test_results( int /*test_case_idx*/ )
             sq0 += v0*v0;
             sq1 += v1*v1;
             result0[CV_COMP_BHATTACHARYYA] += sqrt(v0*v1);
+            {
+            if( fabs(v0) <= DBL_EPSILON  )
+                continue;
+            if( fabs(v1) <= DBL_EPSILON )
+                v1 = 1e-10;
+            result0[CV_COMP_KL_DIV] += v0 * std::log( v0 / v1 );
+            }
         }
     }
     else
@@ -1046,6 +1053,13 @@ int CV_CompareHistTest::validate_test_results( int /*test_case_idx*/ )
             s0 += v0;
             sq0 += v0*v0;
             result0[CV_COMP_BHATTACHARYYA] += sqrt(v0*v1);
+            {
+            if (v0 <= DBL_EPSILON)
+                continue;
+            if (!v1)
+                v1 = 1e-10;
+            result0[CV_COMP_KL_DIV] += v0 * std::log( v0 / v1 );
+            }
         }
 
         for( node = cvInitSparseMatIterator( sparse1, &iterator );
@@ -1076,7 +1090,8 @@ int CV_CompareHistTest::validate_test_results( int /*test_case_idx*/ )
             i == CV_COMP_CHISQR_ALT ? "Alternative Chi-Square" :
             i == CV_COMP_CORREL ? "Correlation" :
             i == CV_COMP_INTERSECT ? "Intersection" :
-            i == CV_COMP_BHATTACHARYYA ? "Bhattacharyya" : "Unknown";
+            i == CV_COMP_BHATTACHARYYA ? "Bhattacharyya" :
+            i == CV_COMP_KL_DIV ? "Kullback-Leibler" : "Unknown";
 
         if( cvIsNaN(v) || cvIsInf(v) )
         {