| Author(s) | Collection number | Pages | Download abstract | Download full text |
|---|---|---|---|---|
| Lutskiv M. M., Huk I. B., Федина Б. І. | № 2 (65) | 57-67 |
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A mathematical model of tone reproduction during de-rasterisation with round elements is developed, which is based on the Yule-Nielsen demodulation formula, normalised raster transformations and the proposed local contrast. The raster density of the demodulation of the nonlinear raster transformation is determined for elements of round shape, the characteristic of which is an inclined S-shaped curve. It is established that the shape of the demodulation curve is determined by the accepted law of change of the raster element area and, therefore, by the tone reproduction of a specific image (light, grey, dark). The deviation of the raster density characteristic of the demodulation of the raster transformation for round elements from the linear one is determined and it is established that the demodulation brightens light tones and darkens grey ones. A structural diagram of the demodulation and contrast simulator model is constructed in the Matlab:Simulink package, which makes it possible to simultaneously calculate and construct the gradation characteristics of tone reproduction during demodulation, the characteristics of local contrast, and analyse the properties of raster tone reproduction.
The results of simulation modelling are presented in the form of gradation characteristics of raster transformation demodulation, expressed by raster densities in which the relative area changes according to linear and nonlinear rasterisation algorithms. It is suggested to assess the demodulation characteristic by the deviation from the linear one, which is a sinusoidal curve with a minimum deviation of -9.177% and a maximum value of +19.62%. The local contrast of tone reproduction is determined, which depends on the tone transfer interval, which for a linear law of area change gradually increases from 1.7 to 10.15 units, and for a non-linear change it is in the range from 0.71 to 10.63 units over the entire tone transfer interval. It is established that on the average range of tone transfer, with an area of elements 0.6≤S≤0.4, the relative contrast is in the range of 0.7≤Ко≤0.128, which gives an objective estimate of the contrast, on the other hand, with a small area, on light tones, the relative contrast gives an unreliable estimate of demodulation of raster transformation.
Keywords: modelling, demodulation, rasterisation, round element, simulator, characteristics, local contrast, quality.
doi: 10.32403/1998-6912-2022-2-65-57-67
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