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copied!<p>Well, basically you need to detect <strong>circles</strong>. Have you seen <code>cvHoughCircles()</code>? Are you allowed to use it?</p> <p>This page has good info on how <a href="http://cgi.cse.unsw.edu.au/~cs4411/wiki/index.php?title=OpenCV_Guide" rel="noreferrer">detecting stuff with OpenCV</a>. You might be more interested on <a href="http://cgi.cse.unsw.edu.au/~cs4411/wiki/index.php?title=OpenCV_Guide#Detecting_circles" rel="noreferrer">section 2.5</a>. </p> <p>This is a small demo I just wrote to detect coins in this picture. Hopefully you can use some part of the code to your advantage.</p> <p><strong>Input</strong>: <img src="https://i.stack.imgur.com/hoD2b.jpg" alt="input img"></p> <p><strong>Outputs</strong>: <img src="https://i.stack.imgur.com/Zfss9.png" alt="output opencv img"></p> <pre><code>// compiled with: g++ circles.cpp -o circles `pkg-config --cflags --libs opencv` #include <stdio.h> #include <cv.h> #include <highgui.h> #include <math.h> int main(int argc, char** argv) { IplImage* img = NULL; if ((img = cvLoadImage(argv[1]))== 0) { printf("cvLoadImage failed\n"); } IplImage* gray = cvCreateImage(cvGetSize(img), IPL_DEPTH_8U, 1); CvMemStorage* storage = cvCreateMemStorage(0); cvCvtColor(img, gray, CV_BGR2GRAY); // This is done so as to prevent a lot of false circles from being detected cvSmooth(gray, gray, CV_GAUSSIAN, 7, 7); IplImage* canny = cvCreateImage(cvGetSize(img),IPL_DEPTH_8U,1); IplImage* rgbcanny = cvCreateImage(cvGetSize(img),IPL_DEPTH_8U,3); cvCanny(gray, canny, 50, 100, 3); CvSeq* circles = cvHoughCircles(gray, storage, CV_HOUGH_GRADIENT, 1, gray->height/3, 250, 100); cvCvtColor(canny, rgbcanny, CV_GRAY2BGR); for (size_t i = 0; i < circles->total; i++) { // round the floats to an int float* p = (float*)cvGetSeqElem(circles, i); cv::Point center(cvRound(p[0]), cvRound(p[1])); int radius = cvRound(p[2]); // draw the circle center cvCircle(rgbcanny, center, 3, CV_RGB(0,255,0), -1, 8, 0 ); // draw the circle outline cvCircle(rgbcanny, center, radius+1, CV_RGB(0,0,255), 2, 8, 0 ); printf("x: %d y: %d r: %d\n",center.x,center.y, radius); } cvNamedWindow("circles", 1); cvShowImage("circles", rgbcanny); cvSaveImage("out.png", rgbcanny); cvWaitKey(0); return 0; } </code></pre> <p>The detection of the circles depend a lot on the parameters of <code>cvHoughCircles()</code>. Note that in this demo I used Canny as well.</p>

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