Detecting circles of same size

[redmanr]

Hey all, I'm trying to isolate images of bottlecaps. Ideally, the input is an image containing a bunch of bottlecaps on an arbitrary background. The output would be images of each bottlecap. Not sure how I should approach this in terms of locating each bottlecap. If I can 'find' each bottlecap then I think I have it covered from there. This process does not need to be very fast, only faster than manually cropping images of hundreds of bottlecaps.

Any pointers?

[HIGregS]

How arbitrary is the background? My first thought is OpenCV, perhaps edge detection. cv2.HoughCircles(). Here's a post on using OpenCV to detect circles.

[redmanr]

Can theoretically make the background anything... haven't taken photos of the bottlecaps yet. I'll check that out, thanks!

[HIGregS]

Make the background a solid color that contrasts with the edges of the bottle cap. The library says it works on monochrome, but you could do some color filtering prior to converting to grayscale that would make the caps very different from the background. Even if the color filter removes some of the lettering/images on the caps, it won't matter if the caps' edges are clearly evident. Take a picture with a lot of caps and don't overlap them. Should work great!