Abstract: Method for producing a raster surface for use in the coloring of a contact lens, in which method an image surface consisting of picture elements is selected, the image surface is subjected to a tonal reduction operation and a threshold tone value is defined for it, and picture elements darker than the threshold value are made black while picture elements lighter than the threshold value are made white, and the black-and-white image surface is subjected to radial stretching in relation to a given point, the position of said point corresponding to the center of the contact lens to be treated, whereupon a raster pattern for the image to be created on the contact lens can be produced using the image surface, i.e. raster pattern thus obtained.