Re: Finding Circles in image.(help needed...)

On Nov 30, 2:18 pm, Manuel Matias <manuel.mat...@xxxxxxxxx> wrote:
On Nov 29, 9:41 pm, Eizo <odpe...@xxxxxxxxx> wrote:



On Nov 29, 10:19 pm, serg271 <serg...@xxxxxxxxx> wrote:

On Nov 29, 7:00 pm, Eizo <odpe...@xxxxxxxxx> wrote:> Hi,
I am looking for some (fast) algorithm to find circles in image.
I understand that there is the usual Matlab routine that use Hugh
transform, but it is slow, and I need some other fast solution.
any ideas?

I would suggest just brute-force it. Make edge detection, or
thresholding/segmentation. After that for each contour (closed edge or
segment boundary) check if it circle or not - for example calculate
center (average) and average radial error. Works pretty well for
convex polygons.

Well, I am using a picture, that isn't super clear (e.g could be
places where the edge isn't closed )
also I think that computing whatever a contour is closed or not is
very time consuming ( correct me if I Am wrong here..)
and I need something that work  very fast.

You don't really need to check if the contour is closed.
The strategy Eizo suggested will work well on a contour
that is _almost_ closed, lacking a small segment
(but not if there is a large segment missing or if the
circunference is broken in two or more places).

Also, you can improve the results in several ways:
- Preprocess the original image to remove noise
- Choose well the edge detector that is better suited
  for your task (sounds like Canny's algorithm might
  help).
- After segmentation, use morphological operations
  (closing should be useful) to have more compact,
  better connected components.

Also, posting an example image will help us with
the specifics of your problem.

Thanks,

the work concentrate mainly on road signs. as such it has to be fast,
also the image is not very good quality, but you can imagine a gray
scale image of a sign, and a little bit of background.

I will try to arrange some good sample.
in the meanwhile if you have more ideas I would love to hear.

E

.

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