fitting a circle to a binary image

Question

I have been using skim age\'s thresholding algorithms to get some binary mask. For example, I obtain binary images like this:

Answer 1

For someone looking to code Mark's suggestion in python, it is quite easy.

collapsed = np.sum(binary_array, axis=0)
# These indices will be already sorted
indices = np.where(collapsed == collapsed.max())[0]
c = indices[int(round((len(indices) - 1) / 2))]

# Same for rows
collapsed = np.sum(binary_array, axis=1)
# These indices will be already sorted
indices = np.where(collapsed == collapsed.max())[0]
r = indices[int(round((len(indices) - 1) / 2))]

# circle center is (r, c)

This code takes care when your shape is not spherical and the collapsing along an axes can have multiple maxima. In that case, it takes the middle one (the one that can give you the largest radius when you fit the circle).