Identifying filled circles in a scanned image

nikie n.estner at
Thu Mar 30 18:42:18 EST 2006

Douglas Douglas schrieb:

> Hi everybody.
> I have a paper form that I scan into an image. My user fills some circles in
> this paper form using black ink. Every form has ten rows with five circles each
> and the user fills only one circle for each row.
> I was wondering if I could use the Python Imaging Library to process these
> forms. I know the Image class is really powerful, but I can't think of a way of
> how to locate wich circle was filled.
> Could anybody please give me an advice on this?

Depends on how much time you have... Google for "Hough Transformation",
or look it up in a text book on image processing. That's a very general
method for finding lines and circles. If you know where the circles
are, comparing the average grey value inside the circle with the
average of the environment should tell you if it's filled or not.

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