Trim scanned images with PIL?

Question

What would be the approach to trim an image that\'s been input using a scanner and therefore has a large white/black area?

Answer 1

For starters, Here is a similar question. Here is a related question. And a another related question.

Here is just one idea, there are certainly other approaches. I would select an arbitrary crop edge and then measure the entropy* on either side of the line, then proceed to re-select the crop line (probably using something like a bisection method) until the entropy of the cropped-out portion falls below a defined threshold. As I think, you may need to resort to a brute root-finding method as you will not have a good indication of when you have cropped too little. Then repeat for the remaining 3 edges.

*I recall discovering that the entropy method in the referenced website was not completely accurate, but I could not find my notes (I'm sure it was in a SO post, however.)

Edit: Other criteria for the "emptiness" of an image portion (other than entropy) might be contrast ratio or contrast ratio on an edge-detect result.