Glass engraving grid
A glass engraving grid is used to break down halftone recordings into printable halftone dots by photographic means and was invented by Georg Meisenbach in 1881 . In printing technology, in principle, it is only possible to print a full tone . In the case of all intermediate or so-called half tones , the human eye is fooled by breaking the full tone into larger or smaller dots, i.e. rasterizing it. This effect is achieved photographically by adding a glass engraving grid.
technology
Thin parallel lines lying close to one another are scratched with a diamond in two round panes of glass and blackened with asphalt. The two glass plates are then cemented together at right angles to each other, creating tiny square windows. In the reproduction camera there is a holding device with graduation for the various rotations of the glass engraving grid, with four-color printing usually 0 ° for yellow (Y), 15 ° for magenta (M), 45 ° for black (K) and 75 ° for cyan ( C). The raster rotation is necessary so that no moiré occurs. The raster disk is located in the camera's beam path a short distance from the film to be exposed.
The distance between the lines in the glass engraving grid is measured in lines per cm (lpcm). For example, one speaks of a 60 grid when there are 60 lines on one cm. Due to the grid spacing between the grid disc and the film, the individual grid point is built up in a circle from the center. So it is darkest in the middle and becomes lighter towards the edge. This is necessary so that the individual tonal values can then be processed with Farmer's attenuator . Until the introduction of electronic image processing, the color separations produced photographically were rarely perfect and had to be touched up manually.
literature
- Helmut Kipphan (Hrsg.): Handbuch der Printmedien. Springer-Verlag, 2000, ISBN 3-540-66941-8 .
Individual evidence
- ↑ a b Basics of raster technology ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. . Retrieved January 17, 2010.
- ↑ Autotypical grid ( memento of the original from January 6, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . Retrieved January 17, 2010.
