Erik M. Buck's latest InformIT article has been posted. The article explains the implementation of real-time video effects processing using the Graphics Processing Unit. A demonstration Xcode project is available.
To apply a green screen effect, shoot a video with a solid colored backdrop. Video processing replaces the backdrop color wherever it can be seen with something else like the image of a weather map. When viewing the final result, action in the foreground appears to take place in front of a weather map that was never there. The demonstration app has been tested with an iPad 2 and an iPod Touch with retina display. It should run well on any iOS device with a camera. The demo doesn’t work in the simulator because the simulator doesn’t provide camera support.