Optical methods development for banknote deterioration evaluation

We have developed a model of the medium color of the image, according to which the image moves away from the viewer at a certain distance, at which all the colors of the image are mixed, forming an inseparable color spot. That is, the image is converted into a conditional pixel, which is a mixture of colors of all its pixels. Based on the proposed model, it is possible to estimate the degree of closeness of the optical characteristics of the two images by the deviation of the average color. The method of medium color was realized with a specially designed program application for Kazakh Tenge as well as for Ukrainian Hryvnia evaluation. The measurement of optical characteristics was performed in the non-printed area near the watermark on both the face and reverse of the banknotes. The results show that the evaluation of the image by the deviation of the medium color according to the developed model is a fairly accurate indicator of wear of the printed layer, has an arithmetic mean error less than traditional optical evaluation methods - brightness change and color difference. Thus, the deviation of the medium color describes the human perception of banknote soiling fairly well. This method of medium color, which aims to eliminate the subjectivity of image evaluation, can be used to process both digital images and imprints.