Array of Histogram Equalization Fractions


These images have been clipped to 384x512 and in this version are stored at half this resolution. A larger version of this array is available.

(Click on any image for enlarged version.)
Local-mean
 subtraction (1,0)(1,0.25)(1,0.5)(1,0.75)Original
 image (1,1)
(0.75,0)(0.75,0.25)(0.75,0.5)(0.75,0.75)(0.75,1)
(0.5,0)(0.5,0.25)(0.5,0.5)(0.5,0.75)(0.5,1)
(0.25,0)(0.25,0.25)(0.25,0.5)(0.25,0.75)(0.25,1)
Full
 histogram equalization (0,0)(0,0.25)(0,0.5)(0,0.75)(0,1)

This is an array of different enhancement processes. Each image was created with a different cumulation function power (alpha) and proportion of local-mean replacement (beta). The top-right image is the original image, equivalent to using alpha=beta=1. The top-left image, local-mean subtraction, was generated with alpha=1, beta=0. The bottom-left image is fully equalized (alpha=beta=0).

One value of alpha was used for each row: 0, 0.25, 0.5, 0.75 and 1 from bottom to top. One value of beta was used for each column: the same sequence from left to right.

The Fourier series method was used with a 41x41 window and 30 terms in each case. Out-of-range values were clipped; these occur most often in images below the bottom-left to top-right diagonal.