Given problem: Spill removal after chroma-key processing. The input is an image with an alpha channel. The transparency was achieved with simple binary chroma-keying, e.g. a pixel is either fully transparent or fully opaque. Now the input image contains spill from the chroma color. Describe an algorithm that can do spill removal for arbitrary chroma colors. The chroma color is known. Describe in enough detail to make it implementable.