From 0154b18a3d32b906e2841ccb214efef5207b207b Mon Sep 17 00:00:00 2001
From: Ilya Lysenkov <no@email>
Date: Wed, 30 Jun 2010 14:37:42 +0000
Subject: [PATCH] Speeded up BruteForceMatcher using matrix multiplication

---
 .../include/opencv2/features2d/features2d.hpp |  3 ++
 modules/features2d/src/descriptors.cpp        | 45 +++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/modules/features2d/include/opencv2/features2d/features2d.hpp b/modules/features2d/include/opencv2/features2d/features2d.hpp
index 6835335400..354537d5e3 100644
--- a/modules/features2d/include/opencv2/features2d/features2d.hpp
+++ b/modules/features2d/include/opencv2/features2d/features2d.hpp
@@ -1872,6 +1872,9 @@ void BruteForceMatcher<Distance>::matchImpl( const Mat& descriptors_1, const Mat
     }
 }
 
+template<>
+void BruteForceMatcher<L2<float> >::matchImpl( const Mat& descriptors_1, const Mat& descriptors_2,
+                                             const Mat& mask, vector<int>& matches ) const;
 
 CV_EXPORTS DescriptorMatcher* createDescriptorMatcher( const string& descriptorMatcherType );
 
diff --git a/modules/features2d/src/descriptors.cpp b/modules/features2d/src/descriptors.cpp
index 362351c025..619a158a60 100644
--- a/modules/features2d/src/descriptors.cpp
+++ b/modules/features2d/src/descriptors.cpp
@@ -41,6 +41,10 @@
 
 #include "precomp.hpp"
 
+#ifdef HAVE_EIGEN2
+#include <Eigen/Array>
+#endif
+
 //#define _KDTREE
 
 using namespace std;
@@ -267,6 +271,47 @@ DescriptorMatcher* createDescriptorMatcher( const string& descriptorMatcherType
 }
 
 
+template<>
+void BruteForceMatcher<L2<float> >::matchImpl( const Mat& descriptors_1, const Mat& descriptors_2,
+                                             const Mat& mask, vector<int>& matches ) const
+{
+    matches.clear();
+    matches.reserve( descriptors_1.rows );
+#if (defined _DEBUG || !defined HAVE_EIGEN2)
+    Mat norms;
+    cv::reduce( descriptors_2.mul( descriptors_2 ), norms, 1, 0);
+    norms = norms.t();
+    Mat desc_2t = descriptors_2.t();
+    for( int i=0;i<descriptors_1.rows;i++ )
+    {
+        Mat distances = (-2)*descriptors_1.row(i)*desc_2t;
+        distances += norms;
+        Point minLoc;
+        minMaxLoc ( distances, 0, 0, &minLoc );
+        matches.push_back( minLoc.x );
+    }
+
+#else
+    Eigen::Matrix<float, Eigen::Dynamic, Eigen::Dynamic> desc1;
+    Eigen::Matrix<float, Eigen::Dynamic, Eigen::Dynamic> desc2;
+    cv2eigen( descriptors_1, desc1);
+    cv2eigen( descriptors_2, desc2 );
+
+    Eigen::Matrix<float, Eigen::Dynamic, Eigen::Dynamic> norms = desc2.rowwise().squaredNorm().transpose();
+    for( int i=0;i<descriptors_1.rows;i++ )
+    {
+        //TODO: it doesn't work in Debug due to assert in lazyAssign
+        Eigen::Matrix<float, Eigen::Dynamic, Eigen::Dynamic> distances = (-2)*desc1.row(i)*desc2.transpose();
+
+        distances += norms;
+        int idx;
+        distances.minCoeff(&idx);
+        matches.push_back( idx );
+    }
+#endif
+}
+
+
 /****************************************************************************************\
 *                                GenericDescriptorMatch                                  *
 \****************************************************************************************/