1. A system implemented on a machine that enables smooth mixing of a foreground region with a subsequent background region of an image, comprising: a component that selects a chain of pixels that defines a contour of the foreground region, the component determines a subpixel area for at least one of the foreground region or a background region of the chain of pixels, the component determines a mixing ratio of a foreground color and a background color, the foreground region smoothly mixed with the subsequent background region based at least in part on the mixing ratio determined at a pixel edge of the contour of the foreground region.