Corner Detection Using cvGoodFeaturesToTrack

Here’s an example opencv application which uses cvGoodFeaturesToTrack to detect corners in a webcam video feed.

// This code displays corners found by the opencv function // GoodFeaturesToTrack (cvGoodFeaturesToTrack) // // Note: I commented out the corner detection using the Harris // algorithm because my computer isn't fast enough to process // both the Harris and the eigenvalue corners in real time. // You can uncomment it and test for yourself. // #include <cv.h> #include <highgui.h> #include <stdio.h> #include <time.h> #define VIDEO_WINDOW "Webcam" #define CORNER_EIG "Eigenvalue Corner Detection" // Disable harris processing //#define CORNER_HARRIS "Corner Detection (Harris)" #define USEC_PER_SEC 1000000L CvScalar target_color[4] = { // in BGR order {​{ 0, 0, 255, 0 }}, // red {​{ 0, 255, 0, 0 }}, // green {​{ 255, 0, 0, 0 }}, // blue {​{ 0, 255, 255, 0 }} // yellow }; // returns the number of usecs of (t2 - t1) long time_elapsed (struct timeval &t1, struct timeval &t2) { long sec, usec; sec = t2.tv_sec - t1.tv_sec; usec = t2.tv_usec - t1.tv_usec; if (usec < 0) { --sec; usec = usec + USEC_PER_SEC; } return sec*USEC_PER_SEC + usec; } struct timeval start_time; struct timeval end_time; void start_timer() { struct timezone tz; gettimeofday (&start_time, &tz); } long end_timer() { struct timezone tz; gettimeofday (&end_time, &tz); return time_elapsed(start_time, end_time); } // A Simple Camera Capture Framework int main(int argc, char *argv[]) { long harris_time; long eig_time; CvCapture* capture = 0; IplImage* curr_frame = 0; // current video frame IplImage* gray_frame = 0; // grayscale version of current frame int w, h; // video frame size IplImage* eig_image = 0; IplImage* temp_image = 0; // Disable harris processing //IplImage* harris_eig_image = 0; //IplImage* harris_temp_image = 0; // Pick one of these capture methods: // You must have compiled opencv with ffmpeg enabled // to use a web stream! //capture = cvCaptureFromFile( // "http://user:pw@192.168.1.101:81/img/video.mjpeg"); //capture = cvCaptureFromAVI( // "http://user:pw@192.168.1.101:81/img/video.mjpeg"); // Capture from a webcam capture = cvCaptureFromCAM(CV_CAP_ANY); //capture = cvCaptureFromCAM(0); // capture from video device #0 if ( !capture) { fprintf(stderr, "ERROR: capture is NULL... Exiting/n"); //getchar(); return -1; } // Create a window in which the captured images will be presented cvNamedWindow(VIDEO_WINDOW, 0); // allow the window to be resized cvNamedWindow(CORNER_EIG, 0); // allow the window to be resized cvMoveWindow(CORNER_EIG, 330, 0); // Disable harris processing //cvNamedWindow(CORNER_HARRIS, 0); // allow the window to be resized //cvMoveWindow(CORNER_HARRIS, 660, 0); // Show the image captured from the camera in the window and repeat while (true) { // Get one frame curr_frame = cvQueryFrame(capture); if ( !curr_frame) { fprintf(stderr, "ERROR: frame is null... Exiting/n"); //getchar(); break; } // Do not release the frame! // Get frame size w = curr_frame->width; h = curr_frame->height; // Convert the frame image to grayscale if( ! gray_frame ) { //fprintf(stderr, "Allocate gray_frame/n"); int channels = 1; gray_frame = cvCreateImage( cvGetSize(curr_frame), IPL_DEPTH_8U, channels); } cvCvtColor(curr_frame, gray_frame, CV_BGR2GRAY); // ==== Allocate memory for corner arrays ==== if ( !eig_image) { //fprintf(stderr, "Allocate eig_image/n"); eig_image = cvCreateImage(cvSize(w, h), IPL_DEPTH_32F, 1); } if ( !temp_image) { //fprintf(stderr, "Allocate temp_image/n"); temp_image = cvCreateImage(cvSize(w, h), IPL_DEPTH_32F, 1); } // Disable harris processing // if ( !harris_eig_image) { // //fprintf(stderr, "Allocate harris_eig_image/n"); // harris_eig_image = cvCreateImage(cvSize(w, h), // IPL_DEPTH_32F, 1); // } // if ( !harris_temp_image) { // //fprintf(stderr, "Allocate harris_temp_image/n"); // harris_temp_image = cvCreateImage(cvSize(w, h), // IPL_DEPTH_32F, 1); // } // ==== Corner Detection: MinEigenVal method ==== start_timer(); const int MAX_CORNERS = 100; CvPoint2D32f corners[MAX_CORNERS] = {0}; int corner_count = MAX_CORNERS; double quality_level = 0.1; double min_distance = 5; int eig_block_size = 3; int use_harris = false; cvGoodFeaturesToTrack(gray_frame, eig_image, // output temp_image, corners, &corner_count, quality_level, min_distance, NULL, eig_block_size, use_harris); cvScale(eig_image, eig_image, 100, 0.00); eig_time = end_timer(); cvShowImage(CORNER_EIG, eig_image); // Disable harris processing // // ==== Corner Detection: Harris method ==== // start_timer(); //// const int MAX_CORNERS = 100; // CvPoint2D32f harris_corners[MAX_CORNERS] = {0}; // int harris_corner_count = MAX_CORNERS; // double harris_quality_level = 0.1; // double harris_min_distance = 1; // int harris_eig_block_size = 3; // int harris_use_harris = true; // // cvGoodFeaturesToTrack(gray_frame, // harris_eig_image, // output // harris_temp_image, // harris_corners, // &harris_corner_count, // harris_quality_level, // harris_min_distance, // NULL, // harris_eig_block_size, // harris_use_harris); // cvScale(harris_eig_image, harris_eig_image, 200, 0.50); // harris_time = end_timer(); // cvShowImage(CORNER_HARRIS, harris_eig_image); // // fprintf(stderr, "harris time: %i eig time: %i/n", harris_time, eig_time); // ==== Draw circles around detected corners in original image //fprintf(stderr, "corner[0] = (%f, %f)/n", corners[0].x, corners[0].y); for( int i = 0; i < corner_count; i++) { int radius = h/25; cvCircle(curr_frame, cvPoint((int)(corners[i].x + 0.5f),(int)(corners[i].y + 0.5f)), radius, target_color[0]); } cvShowImage(VIDEO_WINDOW, curr_frame); // If ESC key pressed, Key=0x10001B under OpenCV 0.9.7(linux version), // remove higher bits using AND operator if ( (cvWaitKey(10) & 255) == 27) break; } // Release the capture device housekeeping cvReleaseCapture( &capture); cvDestroyWindow(VIDEO_WINDOW); cvDestroyWindow(CORNER_EIG); // Disable harris processing // cvDestroyWindow(CORNER_HARRIS); return 0; }