python-imaging/Pillow — pull request #23 by twpayne (2012-12-04 15:47:19+00:00)
Title: Add Image.alpha_composite

This pull request adds `Image.alpha_composite`, an alternative to `Image.blend` that handles opacity better.

See the [Wikipedia article on alpha compositing](http://en.wikipedia.org/wiki/Alpha_compositing). Specifically, this pull requests adds support for the "over" operator.