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.

To produce a screened color separation having any screen angle, an original picture is scanned to generate a set of picture values which are digitized and stored. Also a screen function is generated and stored representing a complete two-dimensional period of a half-tone screen in the form of a grid-like array of grey-tone values, the mesh of the grid-like array being finer than the scanning raster. To expose a reproduction medium, the screen function values are superimposed on the picture values to develop exposure signals for an exposing plotter. The screen angle is selected by virtually rotating the stored screen function data through the selected angle as it is being recalled from memory.

To produce a screened color separation having any screen angle, an original picture is scanned to generate a set of picture values which are digitized and stored. Also a screen function is generated and stored representing a complete two-dimensional period of half-tone screen in the form of a grid-like array of grey-tone values, the mesh of the grid-like array being finer than the scanning raster. To expose a reproduction medium, the screen function values are superimposed on the picture values to develop exposure signals for an exposing plotter. The screen angle is selected by virtually rotating the stored screen function data through the selected angle as it is being recalled from memory.

A method and apparatus for producing rastered printing forms, in which an image pattern is opto-electronically scanned to obtain an image signal, and the printing form production is effected by means of an energy beam recording device controlled by the image signal, whereby the raster points are recorded in a raster network having arbitrary raster angles, by means of relative motion between the printing form and the recording device, in which the pattern to be reproduced is scanned to simultaneously provide image signals for a plurality of adjacent image points of such a pattern, following which, for the control of the recording device, the image signal of that image point is selected whose local position on the image pattern is congruent with the local position of the raster point to be presently recorded, in the formation of the desired raster angles.

Method and apparatus for electromechanically engraving a pattern of diamond shape dot depressions on the surface of a cylindrical printing form in which the pattern predominantly produces lines of ridges particularly useful for textile printing. The pattern is obtained by engraving along successive, parallel, circumferential engraving line paths at an engraving dot rate per cylinder revolution which causes the placement of dots in adjacent lines to be out of phase with each other by an amount substantially different from 180.degree.. The distance between adjacent lines is related to the width of a dot produced at the maximum engraving depth such that adjacent pairs of dots overlap at such engraving depth and produce, even at lesser non-overlapping depths, a pattern which is predominantly a line pattern, i.e., is essentially lineiform.