2 * A Demo to OpenCV Implementation of SURF
3 * Further Information Refer to "SURF: Speed-Up Robust Feature"
5 * liuliu.1987+opencv@gmail.com
20 // define whether to use approximate nearest-neighbor search
27 compareSURFDescriptors( const float* d1, const float* d2, double best, int length )
29 double total_cost = 0;
30 assert( length % 4 == 0 );
31 for( int i = 0; i < length; i += 4 )
33 double t0 = d1[i] - d2[i];
34 double t1 = d1[i+1] - d2[i+1];
35 double t2 = d1[i+2] - d2[i+2];
36 double t3 = d1[i+3] - d2[i+3];
37 total_cost += t0*t0 + t1*t1 + t2*t2 + t3*t3;
38 if( total_cost > best )
46 naiveNearestNeighbor( const float* vec, int laplacian,
47 const CvSeq* model_keypoints,
48 const CvSeq* model_descriptors )
50 int length = (int)(model_descriptors->elem_size/sizeof(float));
52 double d, dist1 = 1e6, dist2 = 1e6;
53 CvSeqReader reader, kreader;
54 cvStartReadSeq( model_keypoints, &kreader, 0 );
55 cvStartReadSeq( model_descriptors, &reader, 0 );
57 for( i = 0; i < model_descriptors->total; i++ )
59 const CvSURFPoint* kp = (const CvSURFPoint*)kreader.ptr;
60 const float* mvec = (const float*)reader.ptr;
61 CV_NEXT_SEQ_ELEM( kreader.seq->elem_size, kreader );
62 CV_NEXT_SEQ_ELEM( reader.seq->elem_size, reader );
63 if( laplacian != kp->laplacian )
65 d = compareSURFDescriptors( vec, mvec, dist2, length );
75 if ( dist1 < 0.6*dist2 )
81 findPairs( const CvSeq* objectKeypoints, const CvSeq* objectDescriptors,
82 const CvSeq* imageKeypoints, const CvSeq* imageDescriptors, vector<int>& ptpairs )
85 CvSeqReader reader, kreader;
86 cvStartReadSeq( objectKeypoints, &kreader );
87 cvStartReadSeq( objectDescriptors, &reader );
90 for( i = 0; i < objectDescriptors->total; i++ )
92 const CvSURFPoint* kp = (const CvSURFPoint*)kreader.ptr;
93 const float* descriptor = (const float*)reader.ptr;
94 CV_NEXT_SEQ_ELEM( kreader.seq->elem_size, kreader );
95 CV_NEXT_SEQ_ELEM( reader.seq->elem_size, reader );
96 int nearest_neighbor = naiveNearestNeighbor( descriptor, kp->laplacian, imageKeypoints, imageDescriptors );
97 if( nearest_neighbor >= 0 )
100 ptpairs.push_back(nearest_neighbor);
107 flannFindPairs( const CvSeq*, const CvSeq* objectDescriptors,
108 const CvSeq*, const CvSeq* imageDescriptors, vector<int>& ptpairs )
110 int length = (int)(objectDescriptors->elem_size/sizeof(float));
112 cv::Mat m_object(objectDescriptors->total, length, CV_32F);
113 cv::Mat m_image(imageDescriptors->total, length, CV_32F);
117 CvSeqReader obj_reader;
118 float* obj_ptr = m_object.ptr<float>(0);
119 cvStartReadSeq( objectDescriptors, &obj_reader );
120 for(int i = 0; i < objectDescriptors->total; i++ )
122 const float* descriptor = (const float*)obj_reader.ptr;
123 CV_NEXT_SEQ_ELEM( obj_reader.seq->elem_size, obj_reader );
124 memcpy(obj_ptr, descriptor, length*sizeof(float));
127 CvSeqReader img_reader;
128 float* img_ptr = m_image.ptr<float>(0);
129 cvStartReadSeq( imageDescriptors, &img_reader );
130 for(int i = 0; i < imageDescriptors->total; i++ )
132 const float* descriptor = (const float*)img_reader.ptr;
133 CV_NEXT_SEQ_ELEM( img_reader.seq->elem_size, img_reader );
134 memcpy(img_ptr, descriptor, length*sizeof(float));
138 // find nearest neighbors using FLANN
139 cv::Mat m_indices(objectDescriptors->total, 2, CV_32S);
140 cv::Mat m_dists(objectDescriptors->total, 2, CV_32F);
141 cv::flann::Index flann_index(m_image, cv::flann::KDTreeIndexParams(4)); // using 4 randomized kdtrees
142 flann_index.knnSearch(m_object, m_indices, m_dists, 2, cv::flann::SearchParams(64) ); // maximum number of leafs checked
144 int* indices_ptr = m_indices.ptr<int>(0);
145 float* dists_ptr = m_dists.ptr<float>(0);
146 for (int i=0;i<m_indices.rows;++i) {
147 if (dists_ptr[2*i]<0.6*dists_ptr[2*i+1]) {
148 ptpairs.push_back(i);
149 ptpairs.push_back(indices_ptr[2*i]);
155 /* a rough implementation for object location */
157 locatePlanarObject( const CvSeq* objectKeypoints, const CvSeq* objectDescriptors,
158 const CvSeq* imageKeypoints, const CvSeq* imageDescriptors,
159 const CvPoint src_corners[4], CvPoint dst_corners[4] )
162 CvMat _h = cvMat(3, 3, CV_64F, h);
164 vector<CvPoint2D32f> pt1, pt2;
169 flannFindPairs( objectKeypoints, objectDescriptors, imageKeypoints, imageDescriptors, ptpairs );
171 findPairs( objectKeypoints, objectDescriptors, imageKeypoints, imageDescriptors, ptpairs );
174 n = ptpairs.size()/2;
180 for( i = 0; i < n; i++ )
182 pt1[i] = ((CvSURFPoint*)cvGetSeqElem(objectKeypoints,ptpairs[i*2]))->pt;
183 pt2[i] = ((CvSURFPoint*)cvGetSeqElem(imageKeypoints,ptpairs[i*2+1]))->pt;
186 _pt1 = cvMat(1, n, CV_32FC2, &pt1[0] );
187 _pt2 = cvMat(1, n, CV_32FC2, &pt2[0] );
188 if( !cvFindHomography( &_pt1, &_pt2, &_h, CV_RANSAC, 5 ))
191 for( i = 0; i < 4; i++ )
193 double x = src_corners[i].x, y = src_corners[i].y;
194 double Z = 1./(h[6]*x + h[7]*y + h[8]);
195 double X = (h[0]*x + h[1]*y + h[2])*Z;
196 double Y = (h[3]*x + h[4]*y + h[5])*Z;
197 dst_corners[i] = cvPoint(cvRound(X), cvRound(Y));
203 int main(int argc, char** argv)
205 const char* object_filename = argc == 3 ? argv[1] : "box.png";
206 const char* scene_filename = argc == 3 ? argv[2] : "box_in_scene.png";
208 CvMemStorage* storage = cvCreateMemStorage(0);
210 cvNamedWindow("Object", 1);
211 cvNamedWindow("Object Correspond", 1);
213 static CvScalar colors[] =
226 IplImage* object = cvLoadImage( object_filename, CV_LOAD_IMAGE_GRAYSCALE );
227 IplImage* image = cvLoadImage( scene_filename, CV_LOAD_IMAGE_GRAYSCALE );
228 if( !object || !image )
230 fprintf( stderr, "Can not load %s and/or %s\n"
231 "Usage: find_obj [<object_filename> <scene_filename>]\n",
232 object_filename, scene_filename );
235 IplImage* object_color = cvCreateImage(cvGetSize(object), 8, 3);
236 cvCvtColor( object, object_color, CV_GRAY2BGR );
238 CvSeq *objectKeypoints = 0, *objectDescriptors = 0;
239 CvSeq *imageKeypoints = 0, *imageDescriptors = 0;
241 CvSURFParams params = cvSURFParams(500, 1);
243 double tt = (double)cvGetTickCount();
244 cvExtractSURF( object, 0, &objectKeypoints, &objectDescriptors, storage, params );
245 printf("Object Descriptors: %d\n", objectDescriptors->total);
246 cvExtractSURF( image, 0, &imageKeypoints, &imageDescriptors, storage, params );
247 printf("Image Descriptors: %d\n", imageDescriptors->total);
248 tt = (double)cvGetTickCount() - tt;
249 printf( "Extraction time = %gms\n", tt/(cvGetTickFrequency()*1000.));
250 CvPoint src_corners[4] = {{0,0}, {object->width,0}, {object->width, object->height}, {0, object->height}};
251 CvPoint dst_corners[4];
252 IplImage* correspond = cvCreateImage( cvSize(image->width, object->height+image->height), 8, 1 );
253 cvSetImageROI( correspond, cvRect( 0, 0, object->width, object->height ) );
254 cvCopy( object, correspond );
255 cvSetImageROI( correspond, cvRect( 0, object->height, correspond->width, correspond->height ) );
256 cvCopy( image, correspond );
257 cvResetImageROI( correspond );
260 printf("Using approximate nearest neighbor search\n");
263 if( locatePlanarObject( objectKeypoints, objectDescriptors, imageKeypoints,
264 imageDescriptors, src_corners, dst_corners ))
266 for( i = 0; i < 4; i++ )
268 CvPoint r1 = dst_corners[i%4];
269 CvPoint r2 = dst_corners[(i+1)%4];
270 cvLine( correspond, cvPoint(r1.x, r1.y+object->height ),
271 cvPoint(r2.x, r2.y+object->height ), colors[8] );
276 flannFindPairs( objectKeypoints, objectDescriptors, imageKeypoints, imageDescriptors, ptpairs );
278 findPairs( objectKeypoints, objectDescriptors, imageKeypoints, imageDescriptors, ptpairs );
280 for( i = 0; i < (int)ptpairs.size(); i += 2 )
282 CvSURFPoint* r1 = (CvSURFPoint*)cvGetSeqElem( objectKeypoints, ptpairs[i] );
283 CvSURFPoint* r2 = (CvSURFPoint*)cvGetSeqElem( imageKeypoints, ptpairs[i+1] );
284 cvLine( correspond, cvPointFrom32f(r1->pt),
285 cvPoint(cvRound(r2->pt.x), cvRound(r2->pt.y+object->height)), colors[8] );
288 cvShowImage( "Object Correspond", correspond );
289 for( i = 0; i < objectKeypoints->total; i++ )
291 CvSURFPoint* r = (CvSURFPoint*)cvGetSeqElem( objectKeypoints, i );
294 center.x = cvRound(r->pt.x);
295 center.y = cvRound(r->pt.y);
296 radius = cvRound(r->size*1.2/9.*2);
297 cvCircle( object_color, center, radius, colors[0], 1, 8, 0 );
299 cvShowImage( "Object", object_color );
303 cvDestroyWindow("Object");
304 cvDestroyWindow("Object SURF");
305 cvDestroyWindow("Object Correspond");