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.

Abstract: A method and apparatus for interactively modifying an image defined by original digital data, representing the color content of pixels of the image at a first resolution. The apparatus comprises a first store (4;12) for storing the digital data of the pixels at the first resolution; a monitor (9); a digitizing table (5); and an image processor (6;13,15). The image processor (6;13,15) is responsive to signals from the digitizing table (5) to select a modification algorithm and a portion of the image stored in the first store (4;12) to which the algorithm is to be applied.

Abstract: This relates to a method of image reproduction in which detail enhancement is carried out using sharp and unsharp signals (S and U), for example in accordance with the expressionP=K (log U- log S)- log Swhere P is the derived picture signal and K is a constant. To reduce the disparity between the fringe amplitudes and steepness on the two sides of a density boundary, the above expression is modified, in accordance with the invention toP=K {log[U+L (U-S)]}-(K+1) log S.Another expression involving the same subtractions of sharp and unsharp signals as the first expression above but in a form suitable for use with signals which have been compressed to represent luminance, is modified in accordance with the invention in a similar way.