MDetermination of contrast sensitivity of gamma transformed dark images

A mathematical model of gamma-transformed images is developed, which makes it possible to calculate the gradation characteristics of digital images of different tonalities, the deviation of characteristics from linear ones, their shift towards worlds, to determine the contrast sensitivity of images, to analyze and compare their properties. In the MATLAB: Simulink package, a structural diagram of the simulator model of gamma-transformed images of different tonality is developed, which simultaneously calculates and constructs the gradation characteristics of their deviation from the linear one. In order to evaluate the gamma properties of transformed images, it is proposed to determine the contrast sensitivity of digital images for various indicators of the transformation degree.

The results of simulated modeling of the gradation characteristics of the trans­formation for indicators of degree r= 1.4 are presented; 2.0; 2.5; 3.0, which correspond to dark tones. It is found that at the beginning of the range, the steepness of the gradation characteristics is the smallest, as a result of which there are losses in the dark tones of the image, but at the end of the interval, the steepness increases, as a result of which the light details of the images are better distinguished. The contrast sensitivity of the image is determined, the initial value of which is equal to zero, smoothly increases to the final values (from 1.394 to 3.00), which quantitatively evaluates the quality of the image on the tone transfer interval.

An increase in r-degree moves the gradation characteristic to the right and down, the images shift to dark tones, instead, the contrast of the images in the worlds increases, the light details in the image are better distinguished. At low values of the power of 1.2 ≤ r ≤ 2.0, the contrast sensitivity decreases, as a result of which the image becomes weak and unclear. The presented characteristics of the deviation of the gradation characteristics from the linear one for different indicators of the degree of gamma, which are concave curves, the amplitude value of which is in the range of -30 to -100 and have a shift to the right towards the worlds.

It is established that the proposed contrast sensitivity objectively evaluates the gamma properties of transformed digital images of different tonality.

The results of the analysis and simulation modeling can be applied in the gamma correction of digital images in computer publishing systems during their preparation for printing, will contribute to the improvement of the quality of printed images of publications.

Keywords: model, gamma transformation, simulation, gradation characteristics, properties, contrast sensitivity, quality.

doi: 10.32403/0554-4866-2023-1-85-22-31