Key extraction by image differentiation

Key extraction is an inverse problem of finding the foreground, the background, and the alpha value from an image and some hints. Although the chromakey solves this for a limited case (single background color), this is often too restrictive in practical situations. When the extraction from an arbitrary background is necessary this is currently done by a time consuming manual task. To solve the problem, an algorithm must address the unique requirements of the key extraction: high resolution, analytically correct alpha values, and easy human interaction. We present an image differentiation method which, for the first time, fulfills these requirements