Rastering of color-coded images and analysis of parameters influencing clarity in printed production

Abstract

Estimation of influence of parameters of implementation and output of an image in computer publishing system on the received result is given in this paper, the tasks of making up practical recommendations are concerned in relation to optimization of the process of bar image reproducing in the system of element-by-element information processing.

The concept of FM rasterization is based on the fact that randomly located dots cannot cause moire structure. Programs for FM rasterization use complex mathematical algorithms to calculate the optimal, pseudo-random placement of dots so that they do not cause the appearance of artifacts on the image.

It is reasonable to use a frequency-modulated raster for multi-color printing with more than 4 paints using “high fidelity” (hi-fi) technologies, for example, in Hexachrome system using more than four main CMYK paints, adding the fifth (orange) and the sixth (green) paint. At the same time, the latter should divide the angles of the raster with two of the four triad paints, usually blue and yellow, and in such conditions moire arises inevitably. FM rasterization eliminates this problem.

Traditional rasterization, called amplitude modulated (AM), where amplitude means the area of a dot, imitates the semitones of the original in print due to its division into raster dots of various size and area. In the process of FM rasterization dots, on the contrary, have the same area, and transitions of tones are achieved with the help of frequency variations, or the number of dots per area unit, and their placement. In FM rasterization there are no notions of angles and raster frequency. Dots are placed randomly and do not line up in any directions (i.e. angles). Therefore, this rasterization method is ideal for high-quality multi-color work.

Among disadvantages of irregular rastering it is possible to point out enhanced requirements to the expendable and equipment, technological discipline.

Among specialists there is no consensus as to the best raster. Most often they say that for every plot it is necessary to apply a special raster.