1. A method for generating a geometric mask within a stored color image, comprising the steps of: providing a monitor for displaying the stored color image; providing a coordinate input unit for indicating image coordinates on the monitor and for collecting selected color samples from the color image; providing a color sample memory for representing a three dimensional color space and for storing the selected color samples; providing a two dimensional mask memory for storing at least one mask; providing a color computer for correcting color values of the stored color image and for generating the mask; providing in addition to said color sample memory a separate image store for storing the color image; collecting color samples from the color image with the coordinate input unit; storing the collected color samples in said color sample memory; displaying an arrangement of the color samples in a color space on a monitor with a color coordinate system; subjecting the collected color samples to a filtering to fill undesired gaps between the color samples if such undesired gaps are present, a color sample space produced by the filtering having an arbitrary shape; writing an extreme value into the color computer at locations in the color space defined by the color sample space and applying image data of the color image to the color computer; comparing output data of the color computer to a threshold; setting a memory cell in the mask memory when the comparison to the threshold shows that color data belong to one of the color samples; and displaying the geometric mask generated in the above steps in the image on the monitor.