Point closure

The point circuit (English "dot touch") denotes a position in the representation of a raster image (film, record, print) on the two adjacent color dots of an image in a printing raster adjoin each other. One also speaks of connecting adjacent grid points.

If different tonal values ​​are represented by means of variable size uniformly tinted color dots in a print raster with a fixed ruling (an amplitude-modulated raster, AM raster, so-called autotypical raster), dot closure occurs from a certain degree of area coverage, which depends on the shape of the dots. In the case of the dot shape of a chain grid (60 grid), the dot closure is, for example, around 40 to 60% tonal value. If the point size increases steadily, a break occurs in the curve of the increase in tone value when the point closure occurs, since above this value an increase in the points due to the overlap with the neighboring points results in less increase in the area coverage of the points. The use of elliptical instead of circular pressure points, for example, results in two point closure values ​​and thus a distribution over two less pronounced breaks in the tone value curve, so that the tone value jumps and breaks are attenuated at point closure. Another possibility of damping is the detachment of individual pixels from the raster point in order to place them elsewhere ( dithering ). For this purpose, the area around the grid point must also be included in the calculation (super cell).

literature

• Helmut Teschner: Specialist dictionary digital and print media . Christiani, Konstanz 2008, ISBN 978-3-86522-384-5 .