Identifying filled circles in a scanned image

[Terry Reedy]

"> Douglas Douglas <replaceafill at yahoo.com> writes:
>
>> 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.

I though about this problem once but never had occasion to do anything 
concrete.  The key is to have some landmarks on the paper form that the 
analysis program can find.  One can then convert between printed image 
coordinates and scanned image coordinates.  This corrects for both 
variations in image placement on the sheet and sheet placement on the 
scanner.

Terry Jan Reedy