Chroma Key

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I've never used OpenCV before... Would it be possible to code a "perfect" chroma key (green screen) application with it?

1. At the basic level I need to set the alpha channel on all the pixels that match a particular RGB value (i.e. 51-255-0 aka green) to be transparent.
2. Set a range for other colors that are close to green (but not EXACTLY 51-255-0) to also be transparent.
3. Set pixels to be "semi-transparent" - So, remove the green out of them, but not the brown (for example). This is needed for the edge of the subject, mainly hair. Or semi-transparent objects such as glass.

Here is what I'm trying to achieve:

• Before: http://www.ultimatte-software.com/images/close-shot-blue-screen.jpg
• After: http://www.ultimatte-software.com/images/close-shot-composite-ultimatte.jpg

Thanks!