python library to find outline of image

I am working with Python and PyQt4. I am looking a library with which I can find the outline path of an image (bitmap). With "outline path" I mean a polygon, which separates filled (non-transparent) pixels in the middle of the image from transparent pixels surrounding them.

I can not find anything via google, which kind of开发者_StackOverflow社区 makes me wonder if I am using the correct search terms.

Thanks!

There are similar questions here on Stack Overflow which may be of use... ? Essentially you're trying to do edge detection; try searching for that..

OpenCV has a function called FindContours which does what I want.