On a method of the analysis of digital image using histograms

Histograms are usually used to analyze brightness and contrast characteristics of digital images. Brightness histogram is a discrete function which puts each level of brightness into correspondence with the amount of pixels that have the brightness level. It is possible to divide images into four categories using brightness characteristics. They are dark, bright, low contrast, high contrast. Histograms corresponding to such images are characterized by the way the majority of nonzero values of the histogram is arranged. Contrast histogram is a discrete function which puts each level of contrast (an absolute value of the difference of two pixels’ brightnesses) into correspondence with the amount of pixels that have the contrast level. Mathematical expectation and brightness and contrast dispersion are used in addition to the brightness and contrast histograms which are calculated using correspondent histograms. The proposed method used contrast histograms that were built by comparing each pixel’s brightness with the average brightness of the 8 surrounding pixels. Histogram forms for images with increased and reduced contrast were found during the analysis of such contrast histograms. As a result a mathematic equation which allows calculating contrast level of an image using the contrast histogram was obtained.