Generalized Differential Graylevel Histogram Equalization Histogram equalization (HE) is a simple and effective method for contrast enhancement as it can automatically define the graylevel transformation function based on the distribution of graylevel included in the image. HE fails to produce satisfactory results for broad range of lowcontrast images because the HE does not use a spatial feature included in the input image. The differential graylevel histogram which is contained edge information of the input image, were defined. Furthermore, the differential graylevel histogram equalization (DHE) has been proposed. The DHE shows better enhancement results compared to the HE results for many kinds of images. In this paper, we propose a generalized DHE (GDHE) method. In GDHE, histograms are created using powers of gradients. If the power is set as 0, GHE is equivalent to HE, and if the power is set as 1, GHE is equivalent to DHE. That is, GDHE includes HE and DHE. GHE can preserve the mean brightness of the input image perfectly by setting the power appropriately and shows good contrast enhancement results at the same time.

Wireless Capsule Endoscopic Image Enhancement Method Based on Histogram Correction and Unsharp Masking in Wavelet Domain Due to the limited illumination and complex environment in the gastrointestinal (GI) tract, endoscopic images are usually not clear enough to be interpreted by doctors or used for further processing. In order to solve this problem, a method based on histogram correction and unsharp masking in the wavelet domain is proposed in this paper, to improve the contrast and reveal details of endoscopic images. The HSI color space is adopted for color naturalness, and a logarithm based histogram correction method (LHCM) is proposed to improve the contrast and avoid aritifacts. Details are further enhanced by unsharp masking. Experimental results show that performance of the proposed method is better compared with the stateofart methods. It can be applied to general images and have good effects as well.