How to remove UIImage Background color and make it transparent using Coregraphics?

Withou开发者_开发技巧t using photoshop how to remove image background color and make it transparent using Coregraphics..

As far as I know you are not able to magically remove a background from a photo. How would you know what to remove and what not? You are, however, able to perform some masking on an image, "transforming" it's shape (read http://iosdevelopertips.com/cocoa/how-to-mask-an-image.html).