Abstract: A method for dot-size correction or modification in half-tone colour separations to be used in the production of printing plates for printing reproductions of coloured originals in which a contact print is overexposed through a photographic mask constituted so as to isolate a selected area in addition to being exposed normally for obtaining an exact copy of an original half-tone separation. The mask is generated electronically using an electrical signal obtained by scanning each separation, digitizing each signal and storing the digital values in a digital storage device. A halftone separation is visualized electronically as an image in a dislay device, e.g., video tube, an area of said image is defined for isolation and correction and the combination of positive and/or negative separations required to serve as a mask effective for isolating the selected area for purposes of dot evaluation is determined via a look-up table.