prepress wiki


In most processes in multicoloured printing it is only possible purely technically to print a particular position with one printing ink or not. Apart from in gravure lighter colour tones or mixes cannot be produced directly. To produce halftones, the principle of screening is worked with. In this case, analogue information, such as saturation or tonal value, is converted into a binary image information so that it can be implemented in printing technology. Through the screening the printing image is divided into screen dot with a particular distance (screen resolution). The human eye observes a particular colour value at a given distance depending on how many colour dots are collected together. The screen resolution and the size of the screen dots are decisive here. The individual printing points can be square or round, but do have to have a certain minimum size. This can be problematic with thin lines, small fonts or light hues. To avoid unwanted overcuttings of different screen dots (incorrect colours) or moiré effects the colour separations in different angles (screen angle) are imposed on each other.


A distinction is made between autotype and frequency-modulated screening.


Image left: In autotypical screening tonal values are produced through the different sizes of the screen dots. Their midpoints are always equidistant from each other. Depending on the size the screen dots cover a particular part of a picture position and thus appear lighter or darker optically.


Image right: In frequency modulated screening tonal values through the varying density of screen dots of the same size. 

                                  Autotypical screening                                                                                                                 Frequency modulated screening
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