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Detecting small colored spheres

Hi guys,

I recently started with openCV and since this is a very powerful library I was wondering if someone can give me some advice in which direction I should be heading. I want to detect small colored spheres like marbles and I was wondering which combination of algorithms are best suited for this purpose. Since this should run on a mobile device I have also to take the performance into account and that the camera won't be static.

Any help is highly appreciated

Detecting small colored spheres

Hi guys,

Any help is highly appreciated

Update

I did not completely solve this problem but since I made some progress I figured I post it here as an answer.

For the first testcase I try to detect a yellow marble using an iPhone 4S. I am using HSV and findContours which already gave me some great results.Later on I am also deleting some noise by iterating over the contour vector<vector> and erasing contours with big or very small size().

cv::Mat thresholdHSV;
cv::Mat imgHSV;
cv::Mat fu;

cv::cvtColor(inputFrame, imgHSV, CV_BGR2HSV);

cv::inRange(imgHSV,cv::Scalar(20,100,100),cv::Scalar(30,255,255),thresholdHSV);

std::vector<std::vector<cv::Point> > contours;

findContours(thresholdHSV.clone(), contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);
 //Draw them
cv::Mat dst = cv::Mat::zeros(inputFrame.size(), inputFrame.type());
drawContours(dst, contours, -1, cv::Scalar(255,0,0), CV_FILLED);

However sometimes there is still noise which gets displayed so I figured since the image is so much reduced and the marble is a perfect circle, HoughCircle can give me the best result. Unfortunately I can't just use dst(from the above code) for an input for HoughCircle (not 8bit single channel).I also tried this with no matches:

HoughCircles(thresholdHSV, detectedCircles, CV_HOUGH_GRADIENT, 1, thresholdHSV.rows / 8, 200, 100, 0, 0);

I also tried to smooth the image with no result. Since the image is so much reduced, I thought there must be away to use HoughCircles on it in a performant way.

Another thought was using

void minEnclosingCircle(InputArray points, Point2f& center, float& radius)

and somehow comparing the enclosing circle to the contours,(but thats actually what this is doing so...)

I really hope you guys can help me and thanks for your time.