CODEWITHSUNDEEP
c++opencv
SSteve
SSteve

Reputation: 10698

OpenCV's findCirclesGrid isn't finding a grid of circles

I'm trying to perform a camera calibration with a grid of circles. I've been unsuccessful because findCirclesGrid always returns false even with a file that is nothing but a grid of circles. I've boiled it down to this simple program:

#include <iostream>

#include "opencv2/core.hpp"
#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/calib3d.hpp"

using namespace std;
using namespace cv;

int main(int argc, char *argv[]) {
    Mat image;
    // read an image
    if (argc < 2)
        image = imread("circleGridSmall.jpg");
    else
        image = imread(argv[1]);

    if (!image.data) {
        cout << "Image file not found\n";
        return 1;
    }

    imshow("image", image);
    waitKey(0);

    bool found;
    vector<Point2f> pointbuf;

    found = findCirclesGrid( image, Size(8, 12), pointbuf); 
    printf("found: %d\n", found);
    return 0;
}

And this simple image:

grid of circles

Even with this, findCirclesGrid returns false. What am I missing?

Upvotes: 2

Views: 10970

Answers (2)

Paulus
Paulus

Reputation: 1457

If it works at one size and not at another, then your size filtering on the blobs is tripping you up. You need to create a custom blob detector, which you tweak with min size, max size, circularity etc.. (although size is probably the one affecting you), then pass the custom blob detector as an optional parameter into your findCirclesGrid() function.

Anther thing I have found useful is to experiment with opencv and its python bindings. Turnaround time is a lot quicker than recompiling each time while you experiment with such things, then when you have it sussed out, you solidify the design into c++ code.

Upvotes: 2

O&#39;Neil
O&#39;Neil

Reputation: 3849

You have inverted the points_per_row and points_per_colum in Size() function.
According to the documentation of function findCirclesGrid(), 2nd parameter patternSize is

Size(points_per_row, points_per_colum)

Theferore:

// not 
found = findCirclesGrid( image, Size(8, 12), pointbuf); 
// but
found = findCirclesGrid( image, Size(12, 8), pointbuf);

Upvotes: 3

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