Generating half-tone representations

Abstract

A method and apparatus for generating a half-tone representation of an original image is described. The apparatus comprises an exposing beam generator (8); a record medium support (11); and a mirror (10) for causing an exposing beam generated by the beam generator (8) to scan a record medium mounted on the support (11). An exposing beam control system (5) generates a two state control signal (CS) to control the condition of the exposing beam, the control signal being generated in accordance with a picture signal (PS) representing color component densities of the original image and half-tone dot information (PV) defining for elemental areas within a dot cell corresponding values representative of color densities whereby elemental areas of the record medium are exposed or not exposed in use according to the control signal taking up a first or second state respectively. The control signal is generated by making use of a probability function which introduces a random element into the choice of elemental areas at the edge of a half-tone dot, but which ensures that, although each half-tone dot will not itself accurately define the required color density, an area of such dot will on average define the required dot density with the further feature that within that area, the dots will have a variety of different shapes.