1. A method for determining an alpha value for a candidate pixel of an image in an alpha matting process, the method comprising: selecting two or more pairs of foreground pixels and background pixels; for each pair of foreground pixel and background pixel, calculating an associated alpha value based on a color of the foreground pixel and a color of the background pixel; for each pair of foreground pixel and background pixel, calculating a probability function based on the associated alpha value, wherein the probability function is modeled by assuming two or more characteristics of the pixels as statistically independent; determining the pair of foreground pixel and background pixel with the highest value of the probability function; and setting the alpha value for the candidate pixel to the associated alpha value of the determined pair of foreground pixel and background pixel, wherein a cost function is derived from the probability function such that determining the lowest value of the cost function is equivalent to determining the highest value of the probability function, wherein the cost function employs an alpha-dependent weighting of spatial costs, and wherein the alpha-dependent weighting is defined such that for a pixel being estimated as pure background the influence of the spatial distance of a foreground candidate is minimal, and that for a pixel being estimated as pure foreground the influence of the spatial distance of a background candidate is minimal.