Revision history [back]

Some findings:

Size must be odd in both dimensions (this makes sense when you consider how the found circles are ordered)
Using an adaptive threshold (with a blockSize ~3x the circle size works well for me)
The Size is supposed to be number of items per row, then number of rows (not the other way around as some suggest)
For assymetric circles, each row is a straight line of circles

Here's my code.... (i'm running inside openFrameworks, hence image.getPixelsRef():

Mat cvImage;
cvtColor(toCv(this->image.getPixelsRef()), cvImage, CV_RGB2GRAY);

int blockSize = sqrt(this->paramMaxArea) * 3.0f;
blockSize = (blockSize / 2) * 2 + 1;
if (blockSize <= 1) {
    blockSize = 3;
}

adaptiveThreshold(cvImage, cvImage, 255, ADAPTIVE_THRESH_GAUSSIAN_C, THRESH_BINARY, blockSize, 2);

imitate(this->thresholdedImage, cvImage);
memcpy(this->thresholdedImage.getPixels(), cvImage.data, this->thresholdedImage.getPixelsRef().size());
this->thresholdedImage.update();

SimpleBlobDetector::Params params;
params.maxArea = paramMaxArea; // 100 * 100
params.minArea = paramMinArea; // 10 * 10
Ptr<FeatureDetector> blobDetector = new SimpleBlobDetector(params);

auto success = findCirclesGrid(cvImage, cv::Size(5, 7), this->centers, CALIB_CB_ASYMMETRIC_GRID | CALIB_CB_CLUSTERING, blobDetector);
cout << (success ? "success" : "fail") << endl;

Here's the image i'm testing with: http://www.kimchiandchips.com/files/opencv/5x7.JPG (i can't attach directly here since it's larger than 1MB)

And here's a screenshot of the app running: C:\fakepath\Screen Shot 2014-10-02 at 23.52.34.png

The full code can be found at: this gist

Some findings:

Size must be odd in both dimensions (this makes sense when you consider how the found circles are ordered)
Using an adaptive threshold (with a blockSize ~3x the circle size works well for me)
The Size is supposed to be number of items per row, then number of rows (not the other way around as some suggest)
For assymetric circles, each row is a straight line of circles

Here's my code.... (i'm running inside openFrameworks, hence image.getPixelsRef():

Mat cvImage;
cvtColor(toCv(this->image.getPixelsRef()), cvImage, CV_RGB2GRAY);

int blockSize = sqrt(this->paramMaxArea) * 3.0f;
blockSize = (blockSize / 2) * 2 + 1;
if (blockSize <= 1) {
    blockSize = 3;
}

adaptiveThreshold(cvImage, cvImage, 255, ADAPTIVE_THRESH_GAUSSIAN_C, THRESH_BINARY, blockSize, 2);

imitate(this->thresholdedImage, cvImage);
memcpy(this->thresholdedImage.getPixels(), cvImage.data, this->thresholdedImage.getPixelsRef().size());
this->thresholdedImage.update();

SimpleBlobDetector::Params params;
params.maxArea = paramMaxArea; // 100 * 100
params.minArea = paramMinArea; // 10 * 10
Ptr<FeatureDetector> blobDetector = new SimpleBlobDetector(params);

auto success = findCirclesGrid(cvImage, cv::Size(5, 7), this->centers, CALIB_CB_ASYMMETRIC_GRID | CALIB_CB_CLUSTERING, blobDetector);
cout << (success ? "success" : "fail") << endl;

Here's the image i'm testing with: http://www.kimchiandchips.com/files/opencv/5x7.JPG (i can't attach directly here since it's larger than 1MB)

And here's a screenshot of the app running: ~~C:\fakepath\Screen Shot 2014-10-02 at 23.52.34.png~~Screen Shot

The full code can be found at: this gist