Abstract: For presetting values of parameters in an image-reproducing process, an operator selects a spot on a transparency to be reproduced, for example by visual inspection of a projected image of an area of the transparency illuminated by a defocused light beam. The light beam is then temporarily brought to a focus on the selected spot and the light transmitted through the transparency on a photomultiplier, the signal from which is sampled within a very short period and held, after which the focused light beam is again defocused to enable the operator to select a further spot. The value of the sample signal is used in the presetting of the said parameter values. The period for which the focused light beam falls on the transparency is made small enough to avoid the bleaching of the transparency at the illuminated spot.

Abstract: In the reproduction of a half-tone image, x and y pulse trains are generated in synchronism with the production of image-representing signals resulting from scanning the image to be reproduced; the x pulse train is multiplied in frequency by first and second factors and the y pulse train by third and fourth factors, all factors being irrational or nearly irrational and being different functions of the screen angle selected for printing; the first and third pulse trains are accumulated and combined and the second and fourth pulse trains are separately accumulated and combined, the resulting signals being applied to a function generator which produces a predetermined screen pattern signal which is a periodic two-dimensional function of the position of the scanned image element in the two mutually perpendicular directions.