Simulation of light images demodulation synthesized by the raster elements area

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Lutskiv M. M., Федина Б. І., Шевчук О. В. № 1 (66) 23-31 Image Image

A mathematical model of the demodulation of light tone images synthesized by the raster elements area is developed, which is based on the Yule-Nielsen formula and serves for the visual assessment of the integral (raster) density based on the optical density of the ink layer of the plate, the optical density of the paper and a coefficient that takes into account a specific raster lineature, synthesized by the corrected relative area of raster elements. A structural diagram of the demodulation model is constructed in the MATLAB: Simulink package, which makes it possible to correct the relative area of raster elements, to simultaneously calculate and form the gradation characteristics of tone reproduction in the areas, and to analyze their properties.

Examples of the simulation modeling results of the correction of the raster elements areas for various indicators of degrees r=0.2 and r=0.4, the characteristics of which are convex curves, are shown. The presented gradation characteristics of the synthesized tone reproduction have a large steepness at the beginning of the tone reproduction range , which provides contrast and distinction of light images details, and gradually go almost linearly to the specified final density D=2.5. For comparison, the deviation E% of the gradation characteristics from the linear one synthesized for the power indicator r=0.2 is determined, which first rapidly increases to +30%, and then smoothly goes to zero. On the other hand, at the power of r=0.4, the maximum deviation from linearity is +17%, gradually reaches zero, changes its sign and goes towards zero.

It is established that the gradation characteristic of demodulation expressed by the raster density according to the Yule-Nielsen formula corresponds to the characteristic of the gamma corrected areas of the raster elements, scaled (multiplied) by the optical density of DФ plate. The gradation characteristics obtained by different methods are quite close, so they can be used for operational assessment of raster density based on the raster elements area.

Keywords: simulation, rasterization, demodulation, image, synthesis, area correction, gradation characteristic, optical density.

doi: 10.32403/1998-6912-2023-1-66-23-31

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