I have some doubts about cvHoughCircles parameters. I have an image that has some circles and I want to count them, the count gives me a wrong number of circles.
So I don't know how to choose some function's parameters like:
dp,min_dist,param1,param2,min_radius, max_radius.
I don't know what numbers I use in this parameters. How Can I calculate this?
Choosing the parameters depends on the images you are using. An explanation of the parameters themselves can be found in the reference here
http://opencv.willowgarage.com/documentation/cpp/imgproc_feature_detection.html#cv-houghcircles
Using the function with the following parameters
HoughCircles(gray, circles, CV_HOUGH_GRADIENT,2, gray->rows/4, 200, 100, 10, 50);
Will make it search for circles with a dp of 2, a minimum distance between the circles of 1/4 of the image and accumulator values of max 200,100 that determine what to accept as a circle. The 10 and 50 are minimum and maximum radius for the circles to accept.
If you have trouble finding these parameters try to make a test program that attaches these values to sliders so you can see the result on a test image.
Especially param2 is something that is difficult to determine by measuring. Because you know how many circles are in your image you can do a parameter crawl in the following way:
for(int i=0;i<200;i++) {
cv::HoughCircles(gray, circles, CV_HOUGH_GRADIENT,2, gray->rows/4, 200, i, 10, 50);
std::cout<<"HoughCircles with param2="<<i<<" gives "<<circles.size()<<" circles"<<endl;
}
I don't know how param1 and 2 are exactly related but you could do the same with a double for loop to find the optimum. The other values need to be measured from the picture. In stead of making a screenshot you can also save this image with the function:
cvSaveImage("image.jpg",gray);
To make sure you are really measuring the exact picture.
