how to detect center of a blurry circle with opencv

Question

I have got the following image:

There are curvs on the picture. i would like to find center of the circles containing curves.

i tried opencv and hough circle transform but had no results.

Answer 1

You'll need to improve the contrast of the image first, then filter it strongly to remove the noise. since the circles are 'thick' (blurry), you can filter quite a bit without destroying the circles structure.

I would then apply some edge detection algorithm to get a binary edge image that can be processed by the Circular Hough Transform.

I get the following edge image from your image:

Using the following MATLAB commands:

 % x is the input grayscale image. First we adaptively improve the contrast over the image
 y= adapthisteq(x);

 % next we use the Canny edge detector with a strong Gaussian lowpass filter
 ee=edge(y, 'canny', [], 5);