1. A method, comprising: performing by a computer: accessing a data representation of an input image and an alpha matte corresponding to the input image, wherein for each pixel in the input image the alpha matte indicates whether the pixel is a foreground pixel, is a background pixel, or is a transition pixel between foreground and background, wherein the transition pixels form a border region between the foreground and the background; for a band of the border region within a distance threshold of a foreground boundary of the border region, determining an estimated foreground color for each pixel within the band, wherein said determining is based on a current color of the pixel and on color values of pixels within a neighborhood distance of the pixel for which foreground colors or estimated foreground color are known; repeating said determining one or more times for one or more successive bands of the border region, wherein each successive band is further from the foreground boundary than the previous band; and creating a composite image based on the foreground pixels of the input image, the estimated foreground colors for the transition pixels, a new background image, and the alpha matte.