Methods and apparatus for half-tone imaging utilizing a rotated

Abstract

An apparatus for controlling the exposure of a record medium (4) to a radiation beam (3) during relative scanning movement between the medium and the beam to record half-tone image separations at particular screen angles, includes a control signal generator (6); a controller (8,9); and a store (7) for storing a previously generated half-tone dot map under the control of the controller (9), the control signal generator being responsive to an image signal representing the color content of an image and a signal from the store to generate a binary beam control signal by scanning the map in synchronism with the beam scanning the record medium and comparing the image signal with the current map value, the binary beam control signal being generated in accordance with the result of the comparison. The store (7) is of a size sufficient to enable the half-tone dot map to define a number of adjacent half-tone dot areas, each area corresponding to a half-tone dot and the content of at least some areas being different. The control signal generator (6) is responsive to each area in the map for generating the control signal for adjacent, corresponding areas on the record medium. The controller (8) scans the half-tone dot map in the same direction and in the same increments for all screen angles and supplies corresponding map values to the control signal generator (6).