Patent ID: 6842268

Claim:
A method, of printing colour images in which a colour image is formed by superimposition of a number of separations, comprising: generating multi-value image signals for each of a number of separations of a colour image, said image signals specifying degrees of coverage for pixels of a separation, respectively, recognising edge transitions in the colour image, which are related to a colour or luminance transition; determining a local transition intensity of an edge transition in each separation; trapping step including determining, for a recognised edge transition, a light and a dark side of the edge transition, determining which separation dominates the edge transition, adjusting the image signals so as to shift the said recognised edge transition in a separation other than the said dominating separation, so that an overlap forms between the light side of the edge transition in the said other separation and the dark side of the edge transition in the dominating separation; and converting the image signals into binary printing signals for pixels of a separation using a first half-tone technique optimised for surface reproduction or a second half-tone technique, differing from the first, optimised for edge reproduction, wherein, in an edge transition, one of said first and second half-tone techniques is selected for each pixel and for each separation on the basis of the extent to which the local transition intensity of the edge transition in that separation influences the edge transition at the location of the pixel concerned.