Extract ellipse(or blob) from an image using OpenCV

Question

I processed an Image to get the image below.

The lines indicates the ellipses(blobs) to be extracted.

I tried cv::findContours function, but the borders extracted together. Please someone help me with my job. Thank you.

Answer 1

I would start by extracting the first/smallest circle, and I would do it like that:

1. basic thresholding to get a binary image.
2. Centroid computation
3. For each path between the centroid and the image border, find the closest non null pixel from the centroid.

These three first step are going to give you the pixels belonging to the first/smallest circle, plus some pixel of the second circle because the first circle is not discontinuous.

5. Hough detection. I think that Hough circle is enough, but in case it does not work, I would use the Ellipsoid version.
6. You keep only the "most likely" circle.