equ_histo_image — Histogram linearization of images
The operator equ_histo_image enhances the contrast. The starting point is the histogram of the input images. The following simple gray value transformation f(g) is carried out for byte images:
This transformation linearizes the cumulative histogram. Maxima in the original histogram are “spreaded” and thus the contrast in image regions with these frequently occurring gray values is increased. Supposedly homogeneous regions receive more easily visible structures. On the other hand, of course, the noise in the image increases correspondingly. Minima in the original histogram are dually “compressed”. The transformed histogram contains gaps, but the remaining gray values used occur approximately at the same frequency (“histogram equalization”).
The operator equ_histo_image primarily serves for optical processing of images for a human viewer. For example, the (local) contrast spreading can lead to a detection of fictitious edges.
Note that filter operators may return unexpected results if an image with a reduced domain is used as input. Please refer to the chapter Filters.
Image to be enhanced.
Image with linearized gray values.
scale_image, scale_image_max, illuminate
R.C. Gonzales, P. Wintz: “Digital Image Processing”; Second edition; Addison Wesley; 1987.