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In order to be able to print differences in brightness on monochromatic printers, the halftone pixel to be printed is divided into individual print dots. Depending on the resolution, a pixel consists of several print dots that are controlled individually. The number of printing dots depends on the physical resolution and the screen frequency.

With this technique, pixels can easily consist of 100 printing dots; in the case of imagesetters for printed documents, even several hundred. The eye integrates all the printing dots into one brightness impression.

Grayscale with ten brightness values, converted into a 3x3 print dot matrix

Grayscale with ten brightness values, converted into a 3x3 print dot matrix

As an example, let us assume that a printer prints a pixel consisting of 100 dots. If a gray value of 20 % is to be printed, then every 5th print dot is printed in black, thus the pixel consists of 20 black print dots. If the gray value is 50 %, every 2nd print point is printed in black. If only ten brightness differences are to be displayed, then a halftone dot consists of a 3x3 print dot matrix. With such a matrix, ten brightness levels between white and black can be represented.

The number of pressure points per pixel thus determines the resolution and also the gradation. With 25 printing dots, 25 different shades of gray can be printed, and with 100 printing dots, 100 shades of gray can be printed.

Englisch: halftoning
Updated at: 01.01.2019
#Words: 219
Links: indium (In), order, brightness, resolution, frequency (f)
Translations: DE

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