In electronic rasterization, the transformation of a halftone image into a raster image is carried out without the use of a photomechanical raster effect, that is, an image of printed elements of a given area is formed in the optical path of the exposure device.
The exposure of the latent image has a rectangular shape distribution (in the shape of the letter P), which after development has a similar distribution of relative densities (blackening) on the photo layer. This distribution is formed in various ways, based on the continuity or discreteness of changes in the area of the resulting points.
In electronic rasterization, exposure density, sensitivity, film contrast, and processing mode affect the density of a point. The size of the point, its sharpness less susceptible to these instabilities than in optical rasterization .
High contrast films are used in electronic screening.
Continuous modulation of the exposure spot area
An image is used to record the image. It serves to create a printing element on a positive photoform, and to create a space on a negative photoform.
Rasterization with continuous control of the light spot area is also called analog.
One of the devices that continuously controls the area of the exposure spot is the electromagnetic diaphragm .
Discrete print size control
Electronic reproduction systems in the digital signal processing technology, computer publishing systems use the methods of discrete changes in the printed area of the raster image. Therefore, discrete control screening is called digital.
Electronic rasterization is carried out in publishing systems by means of computing and laser technology.
The area and shape of printed elements and spaces depends on the quantitative ratio and the location of zeros and units in a set of bitmaps that correspond to a set of raster points.
The raster alphabet can be specified by a matrix of weight values of the same dimension, that is, to create a raster function . Then the contrast signal can be represented as a raster alphabet.
The distribution of weights is orderly and irregular.
Orderly gives a greater number of equal contrast transitions of tone, lightness and saturation, if the values are distributed so that the areas of the elements remain unchanged when transferred to the printing plate, and then to the print. This requirement is satisfied by the distribution in which the weight values monotonously decrease or increase (depending on the given shape of the raster point) from the center to the edges.