SURF ( Speeded Up Robust Features )
Source : OPENCV_PATH\samples\c\find_obj.cpp
Reference : http://en.wikipedia.org/wiki/SURF
Copy from source :
#define USE_FLANN //--------------------------------------------------------- double compareSURFDescriptors( const float* d1, const float* d2, double best, int length ) { double total_cost = 0; assert( length % 4 == 0 ); for( int i = 0; i < length; i += 4 ) { double t0 = d1[i] - d2[i]; double t1 = d1[i+1] - d2[i+1]; double t2 = d1[i+2] - d2[i+2]; double t3 = d1[i+3] - d2[i+3]; total_cost += t0*t0 + t1*t1 + t2*t2 + t3*t3; if( total_cost > best ) break; } return total_cost; } int naiveNearestNeighbor( const float* vec, int laplacian, const CvSeq* model_keypoints, const CvSeq* model_descriptors ) { int length = (int)(model_descriptors->elem_size/sizeof(float)); int i, neighbor = -1; double d, dist1 = 1e6, dist2 = 1e6; CvSeqReader reader, kreader; cvStartReadSeq( model_keypoints, &kreader, 0 ); cvStartReadSeq( model_descriptors, &reader, 0 ); for( i = 0; i < model_descriptors->total; i++ ) { const CvSURFPoint* kp = (const CvSURFPoint*)kreader.ptr; const float* mvec = (const float*)reader.ptr; CV_NEXT_SEQ_ELEM( kreader.seq->elem_size, kreader ); CV_NEXT_SEQ_ELEM( reader.seq->elem_size, reader ); if( laplacian != kp->laplacian ) continue; d = compareSURFDescriptors( vec, mvec, dist2, length ); if( d < dist1 ) { dist2 = dist1; dist1 = d; neighbor = i; } else if ( d < dist2 ) dist2 = d; } if ( dist1 < 0.6*dist2 ) return neighbor; return -1; } void findPairs( const CvSeq* objectKeypoints, const CvSeq* objectDescriptors, const CvSeq* imageKeypoints, const CvSeq* imageDescriptors, vector<int>& ptpairs ) { int i; CvSeqReader reader, kreader; cvStartReadSeq( objectKeypoints, &kreader ); cvStartReadSeq( objectDescriptors, &reader ); ptpairs.clear(); for( i = 0; i < objectDescriptors->total; i++ ) { const CvSURFPoint* kp = (const CvSURFPoint*)kreader.ptr; const float* descriptor = (const float*)reader.ptr; CV_NEXT_SEQ_ELEM( kreader.seq->elem_size, kreader ); CV_NEXT_SEQ_ELEM( reader.seq->elem_size, reader ); int nearest_neighbor = naiveNearestNeighbor( descriptor, kp->laplacian, imageKeypoints, imageDescriptors ); if( nearest_neighbor >= 0 ) { ptpairs.push_back(i); ptpairs.push_back(nearest_neighbor); } } } void flannFindPairs( const CvSeq*, const CvSeq* objectDescriptors, const CvSeq*, const CvSeq* imageDescriptors, vector<int>& ptpairs ) { int length = (int)(objectDescriptors->elem_size/sizeof(float)); cv::Mat m_object(limit_size, length, CV_32F); cv::Mat m_image(limit_size, length, CV_32F); // copy descriptors CvSeqReader obj_reader; float* obj_ptr = m_object.ptr<float>(0); cvStartReadSeq( objectDescriptors, &obj_reader ); for(int i = 0; i < objectDescriptors->total; i++ ) { const float* descriptor = (const float*)obj_reader.ptr; CV_NEXT_SEQ_ELEM( obj_reader.seq->elem_size, obj_reader ); memcpy(obj_ptr, descriptor, length*sizeof(float)); obj_ptr += length; } CvSeqReader img_reader; float* img_ptr = m_image.ptr<float>(0); cvStartReadSeq( imageDescriptors, &img_reader ); for(int i = 0; i < imageDescriptors->total; i++ ) { const float* descriptor = (const float*)img_reader.ptr; CV_NEXT_SEQ_ELEM( img_reader.seq->elem_size, img_reader ); memcpy(img_ptr, descriptor, length*sizeof(float)); img_ptr += length; } // find nearest neighbors using FLANN cv::Mat m_indices(limit_size, 2, CV_32S); cv::Mat m_dists(limit_size, 2, CV_32F); cv::flann::Index flann_index(m_image, cv::flann::KDTreeIndexParams(4)); // using 4 randomized kdtrees flann_index.knnSearch(m_object, m_indices, m_dists, 2, cv::flann::SearchParams(64) ); // maximum number of leafs checked int* indices_ptr = m_indices.ptr<int>(0); float* dists_ptr = m_dists.ptr<float>(0); for (int i=0;i<m_indices.rows;++i) { if (dists_ptr[2*i]<0.6*dists_ptr[2*i+1]) { ptpairs.push_back(i); ptpairs.push_back(indices_ptr[2*i]); } } } /* a rough implementation for object location */ int locatePlanarObject( const CvSeq* objectKeypoints, const CvSeq* objectDescriptors, const CvSeq* imageKeypoints, const CvSeq* imageDescriptors, const CvPoint src_corners[4], CvPoint dst_corners[4] ) { double h[9]; CvMat _h = cvMat(3, 3, CV_64F, h); vector<int> ptpairs; vector<CvPoint2D32f> pt1, pt2; CvMat _pt1, _pt2; int i, n; #ifdef USE_FLANN flannFindPairs( objectKeypoints, objectDescriptors, imageKeypoints, imageDescriptors, ptpairs ); #else findPairs( objectKeypoints, objectDescriptors, imageKeypoints, imageDescriptors, ptpairs ); #endif n = (int)(ptpairs.size()/2); if( n < 4 ) return 0; pt1.resize(n); pt2.resize(n); for( i = 0; i < n; i++ ) { pt1[i] = ((CvSURFPoint*)cvGetSeqElem(objectKeypoints,ptpairs[i*2]))->pt; pt2[i] = ((CvSURFPoint*)cvGetSeqElem(imageKeypoints,ptpairs[i*2+1]))->pt; } _pt1 = cvMat(1, n, CV_32FC2, &pt1[0] ); _pt2 = cvMat(1, n, CV_32FC2, &pt2[0] ); if( !cvFindHomography( &_pt1, &_pt2, &_h, CV_RANSAC, 5 )) return 0; for( i = 0; i < 4; i++ ) { double x = src_corners[i].x, y = src_corners[i].y; double Z = 1./(h[6]*x + h[7]*y + h[8]); double X = (h[0]*x + h[1]*y + h[2])*Z; double Y = (h[3]*x + h[4]*y + h[5])*Z; dst_corners[i] = cvPoint(cvRound(X), cvRound(Y)); } return 1; }
Main code :
iplSrc1 : input image1
iplSrc2 : input image2
correspond : output image
CvMemStorage* storage = cvCreateMemStorage(0); //--------------------------------------------------------- IplImage* image = cvCreateImage( cvGetSize( iplSrc1 ) , IPL_DEPTH_8U , 1 ); IplImage* object = cvCreateImage( cvGetSize( iplSrc2 ) , IPL_DEPTH_8U , 1 ); //--------------------------------------------------------- cvCvtColor( iplSrc1 , image , CV_BGR2GRAY ); cvCvtColor( iplSrc2 , object , CV_BGR2GRAY ); IplImage* object_color = cvCreateImage(cvGetSize(object), 8, 3); cvCvtColor( object, object_color, CV_GRAY2BGR ); CvSeq *objectKeypoints = 0, *objectDescriptors = 0; CvSeq *imageKeypoints = 0, *imageDescriptors = 0; int i; CvSURFParams params = cvSURFParams(500, 1); double tt = (double)cvGetTickCount(); cvExtractSURF( object, 0, &objectKeypoints, &objectDescriptors, storage, params ); cvExtractSURF( image, 0, &imageKeypoints, &imageDescriptors, storage, params ); tt = (double)cvGetTickCount() - tt; CvPoint src_corners[4] = {{0,0}, {object->width,0}, {object->width, object->height}, {0, object->height}}; CvPoint dst_corners[4]; IplImage* correspond = cvCreateImage( cvSize(image->width+object->width, Math::Max( object->height , image->height )), 8, 3 ); cvSetImageROI( correspond, cvRect( 0, 0, object->width, object->height ) ); cvCopy( myCV::iplSrc, correspond ); cvSetImageROI( correspond, cvRect( object->width, 0, correspond->width, correspond->height ) ); cvCopy( myCV::iplObj, correspond ); cvResetImageROI( correspond ); vector<int> ptpairs; #ifdef USE_FLANN flannFindPairs( objectKeypoints, objectDescriptors, imageKeypoints, imageDescriptors, ptpairs ); #else findPairs( objectKeypoints, objectDescriptors, imageKeypoints, imageDescriptors, ptpairs ); #endif for( i = 0; i < (int)ptpairs.size(); i += 2 ) { CvSURFPoint* r1 = (CvSURFPoint*)cvGetSeqElem( imageKeypoints, ptpairs[i+1] ); CvSURFPoint* r2 = (CvSURFPoint*)cvGetSeqElem( objectKeypoints, ptpairs[i] ); cvLine( correspond, cvPointFrom32f(r1->pt), cvPoint(cvRound(r2->pt.x+object->width), cvRound(r2->pt.y)), CV_RGB(255,0,0) ); cvCircle( correspond, cvPointFrom32f(r1->pt), 4, CV_RGB(0,255,0), 1, 8, 0 ); cvCircle( correspond, cvPoint(cvRound(r2->pt.x+object->width), cvRound(r2->pt.y)), 4, CV_RGB(255,255,0), 1, 8, 0 ); }
Output :
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