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 1000000LCvScalar 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 Frameworkint main(int argc, char *argv[]) {long harris_time;long eig_time;CvCapture* capture = 0;IplImage* curr_frame = 0; // current video frameIplImage* gray_frame = 0; // grayscale version of current frameint w, h; // video frame sizeIplImage* 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 webcamcapture = cvCaptureFromCAM(CV_CAP_ANY);//capture = cvCaptureFromCAM(0); // capture from video device #0if ( !capture) {fprintf(stderr, "ERROR: capture is NULL... Exiting/n");//getchar();return -1;}// Create a window in which the captured images will be presentedcvNamedWindow(VIDEO_WINDOW, 0); // allow the window to be resizedcvNamedWindow(CORNER_EIG, 0); // allow the window to be resizedcvMoveWindow(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 repeatwhile (true) {// Get one framecurr_frame = cvQueryFrame(capture);if ( !curr_frame) {fprintf(stderr, "ERROR: frame is null... Exiting/n");//getchar();break;}// Do not release the frame!// Get frame sizew = curr_frame->width;h = curr_frame->height;// Convert the frame image to grayscaleif( ! 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, // outputtemp_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 operatorif ( (cvWaitKey(10) & 255) == 27)break;}// Release the capture device housekeepingcvReleaseCapture( &capture);cvDestroyWindow(VIDEO_WINDOW);cvDestroyWindow(CORNER_EIG);// Disable harris processing//cvDestroyWindow(CORNER_HARRIS);return 0;}