It is a known fact that human beings are more sensitive to edges (contours). It is expected that an enhanced image should have more edge pixels than the original image and this parameter of EBCM does measure the intensity of edge pixels in small windows of the image.

Ref: A. Beghdadi and A. L. Negrate, “Contrast enhancement technique based on local detection of edges,” Comput. Vis. Graph. Image Process., vol. 46, no. 2, pp. 162–174, May 1989.

The easier representation of the below algorithm is also presented in page no. 7/9 of this paper. http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5957283&tag=1