Dr. Ing. Rudolf Hell Gmbh

Intergraph Corporation

Winrich Gall

Klaus Wellendorf

Peter Weselmann

An improved method and apparatus for generating halftone images using a beam of variable intensity. A look-up table that is accessed, at a minimum, by position coordinates and image intensity data provides beam intensity information. In certain embodiments, the look-up table may be accessed by dot set identification data and/or randomly generated numbers in addition to the position coordinates and the image intensity data. The position coordinates (x,y) may be generated by performing a coordinate transformation on the beam position coordinates (u,v). The beam intensity data stored in the look-up table may permit the formation of soft dots, i.e. halftone dots that are formed by different levels of beam exposure. The look-up table also permits an increase in dot frequency in the middle tones.

Improved method and apparatus for generating halftone images

In a method and apparatus for producing half-tone printing forms with screens having arbitrary screen angles and screen width, screen dots are exposed on a recording medium by means of a recording element whose exposure beam is switched on and off by a control signal. The recording medium is sub-divided into a plurality of areal elements which are exposed or not exposed by the exposure beam as a function of the control signal. All areal elements exposed in a screen mesh of the rotated screen to be recorded form a respective screen dot. At least two matrices in the form of matrix memories are provided, the individual matrix elements thereof having screen threshold values allocated to them. The screen threshold values forming a screen hill represent the periodic basic structure of a screen mesh and are different for at least one tonal range in the individual matrices. During recording, those matrix elements in the individual matrices whose positions within the respective matrices correspond to the positions of the swept areal elements within a screen mesh are identified. The screen threshold values of the identified matrix elements are called in. Controlled by a random generator, one of the called screen threshold values is randomly selected and compared to an image signal value acquired by means of scanning an original. The control signal for the exposure beam is derived from the comparison, whereby a decision is made on the basis of the signal comparison as to whether the corresponding areal element is to be exposed or not as part of a screen dot.

Method and apparatus for producing half-tone printing forms with rotated

Method and apparatus for the reproduction of an image with coarser resolution than used during scanning wherein the original image is opto-electronically scanned point-wise and line-wise with a prescribed resolution and is converted into digital image signals, and a field containing as many image points as is used for one coarse image point is extracted from the digital image signals, and wherein weighting is undertaken for the individual image signals of the image points of said field and a corresponding image signal for the coarse image point is obtained by means of combining the weighted image signals.

Method and apparatus for reproducing an image which has a coarser

A method for producing half-tone reproductions such as printing blocks or color separators of an original on a recording medium by means of a recording element using rotated screens having any screen angle and any screen line spacing and being formed of periodically repeated, adjacent screen grid elements comprising screen dots varying in size with the tone values of the original. The recording medium has co-ordinated with it an UV co-ordinate system directed in the line direction and an XY co-ordinate system turned through the screen angle, both co-ordinate systems being subdivided into areal elements from which picture half-tone dots to be produced are collated. Notwithstanding the screen angle, screen threshold values are associated with areal elements of a matrix of limited scanning pattern range which corresponds to at least one screen grid element of the screen which is to be recorded. During the recording operation, the UV locus co-ordinates of the areal elements momentarily traversed by the recording element are recalculated in the form of the corresponding XY locus co-ordinates of the limited scanning range of the matrix and the screen threshold values associated with the XY locus co-ordinates determined are 'called up' from the matrix. A control signal which determines whether the areal element in question is or is not recorded on the recording medium is generated for the recording element by a current comparison of the screen threshold values called up with an image signal obtained by scanning the original.

Production of screen printing blocks

A method of calibrating a reproduction apparatus having a sensor device for generating sensor signals by optically scanning a picture original and a recording device controlled by recording signals for recording the picture original on a film, comprising the steps: generating a set of first signals for said recording device to produce a sample gray scale on the film having a predetermined first range of gray scale values; generating and storing a set of second signals corresponding respectively to said first signals; generating a set of third signals corresponding substantially to the gray scale values of said sample recorded gray scale; correlating said third signals to said first signals; generating a set of fourth signals representing a predetermined second range of gray scale values of a reference gray scale; substantially correlating a first group of at least some of said fourth signals to a second group of at least some of said third signals for obtaining said second signals; and storing said second signals in a storage device having addresses corresponding to the fourth signals of said first group, whereby a substantially generated sensor signal for a given gray scale value by the picture original can be used to select a recording signal from a stored second signal of said second group by a correlated fourth signal suitable for obtaining a substantially duplicate gray scale value. The invention also relates to a system for calibrating the reproduction apparatus.

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Klausdorf, Germany

Winrich Gall