Brightness Preserving Generalized Histogram Equalization
Hideaki Tanaka, Akira Taguchi · 2020
Histogram equalization (HE) is the one of the simplest and most effective methods for contrast enhancement. It can automatically define the gray-level transformation function based on the distribution of gray-level included in the image. However, HE fails to produce satisfactory results for broad range of low-contrast images because the HE does not use a spatial feature included in the input image. The differential gray-level histogram (DH) which is contained edge information of the input image, were defined and the differential gray-level histogram equalization (DHE) has been proposed. The DHE shows better enhancement results compared to the HE result for many kinds of images. In this paper, we propose a generalized histogram equalization (GHE) method including the HE and the DHE. In GHE, the histograms is created using power of gradient including a special feature. In the HE, the mean brightness of the enhancement image cannot be controlled. On the other hand, the GHE can control the mean brightness of the enhancement image by changing the power, thus, the mean brightness of the input image is perfectly preserved.