An apparatus and a method for refining a value of a similarity measure are described. A similarity measure is assigned to a pixel or a group of pixels of a disparity map, which is assigned to at least two stereo images each having a plurality of pixels. The similarity measure constitutes an estimate for a match quality of the pixel or the group of pixels. For refinement of the value of the similarity measure, the similarity measure between a pixel or a group of pixels in a first stereo image and a corresponding pixel or a group of corresponding pixels in a second stereo image is determined. A contrast value for the pixel or the group of pixels of the first or the second stereo image is determined and the value of the similarity measure is corrected by a correction value that is a function of the determined contrast value.