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.)
 subtraction (1,0)(1,0.25)(1,0.5)(1,0.75)Original
 image (1,1)
 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.