SIMULATION OF TONE REPRODUCTION OF DIGITAL RAST IMAGES WITH CHANGE OF PAINT THICKNESS

Abstract

A mathematical model of tonal reproduction of digital raster images for elements of a rhombic shape with a decrease in the thickness of the paint on the tonal transfer interval in combined offset printing systems of a simple design based on an anilox roller, which lacks mechanisms for zonal adjustment of paint supply to a given overlay, has been developed, which makes it possible to perform rasterization of digital images of dark tones and plot the characteristics of the raster transformation, determine the amount of paint on the surface of the raster elements, determine the gradation characteristics of digital images after covering the raster elements with paint, and determine the integral raster optical density of images. In order to simplify the solution of the tasks in the MATLAB: Simulink package, a structural diagram of the model of the simulator for tonal reproduction of digital images with a decrease in paint thickness has been developed, which makes it possible to calculate and build raster characteristics, graphs of the amount of paint on the surface of raster elements and the raster optical density of images, and their results are visualized by the Scope and Display blocks.

The presented results of simulation of the given gradation characteristic of the input digital image of a dark tonality is a slightly concave curve and has a small slope at the beginning of the range, which does not cause posterization in the dark areas of the image, therefore, does not impair the research results. Rhombic raster elements stretch the raster characteristic and shift it to darker tones and darken the details in the dark areas of the image and lighten the light ones. It was established that the decrease in the thickness of the paint on the interval significantly affects the amount of paint on the surface of the raster elements, and therefore the tonality of the image. The initial values of the raster optical density of the image is 2.407 units. A decrease in paint thickness significantly reduces the optical density of the image, and at the beginning of the range at L₀=50 levels, the difference in optical densities is 0.68 units, which is quite large and quantitatively evaluates the effect of changing the paint thickness on the optical density of the image.