Better results with Canny/Hough for circular particles

[Adam Hughes]

Hi,

I have several images of circular particles (see attached for an example)
and I've been experimenting with automatic routines to find edges.

I've found that with Canny, I can get really nice edges, but the edges are
not always connected.  Thus, when I do fill-binary, many of my particles
are not painted in due to slight breaks in the border returned by canny.
 Is there an ideal way to fix this, either by connecting "almost" connected
canny edges?  Additionally, what is the best way to filter out small
fragments and/or non-circular edges?

I've attached an image of the canny outlines; you can see that I obviously
want to get rid some of the regions that aren't associated with any
particles.  PS, the coloring of the outlines are based on the brightness of
the image at that point underneath it, which has been hidden.  (Would be
happy to share the function if anyone wants it).

Lastly, I tried adapting the circular hough transform example:

http://scikit-image.org/docs/dev/auto_examples/plot_circular_elliptical_hough_transform.html

But struggled with setting it up, due to a naive understanding of the
algorithm.  Given that my image has thousands of particles, but I know
roughly the size distribution, would the circular hough transform be useful
to me?

Thanks
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