java - Hough circle detection accuracy very low -

i trying detect circular shape image appears have definition. realize part of circle missing i've read hough transform doesn't seem should cause problem i'm experiencing.

input:

output:

code:

// read image mat src = highgui.imread("input.png");  // convert gray mat src_gray = new mat(); imgproc.cvtcolor(src, src_gray, imgproc.color_bgr2gray);  // reduce noise avoid false circle detection //imgproc.gaussianblur( src_gray, src_gray, new size(9, 9), 2, 2 );  mat circles = new mat();  /// apply hough transform find circles imgproc.houghcircles(src_gray, circles, imgproc.cv_hough_gradient, 1, 1, 160, 25, 0, 0);  // draw circles detected for( int = 0; < circles.cols(); i++ ) {     double[] vcircle = circles.get(0, i);      point center = new point(vcircle[0], vcircle[1]);     int radius = (int) math.round(vcircle[2]);      // circle center     core.circle(src, center, 3, new scalar(0, 255, 0), -1, 8, 0);     // circle outline     core.circle(src, center, radius, new scalar(0, 0, 255), 3, 8, 0); }  // save visualized detection. string filename = "output.png"; system.out.println(string.format("writing %s", filename)); highgui.imwrite(filename, src); 

i have gaussian blur commented out because (counter intuitively) increasing number of equally inaccurate circles found.

is there wrong input image cause hough not work expect? parameters way off?

edit: first answer brought point min/max radius hint hough. resisted adding parameters example image in post 1 of thousands of images varying radii ~20 infinity.

if you'd set minradius , maxradius paramaeters properly, it'd give results.

for image, tried following parameters.

method - cv_hough_gradient mindist - 100 dp - 1 param1 - 80 param2 - 10 minradius - 250 maxradius - 300 

i got following output

• note: tried in c++.