Histograms: 

Histogram Equilization is a process that brings out the color of an image through a computation of the probability distribution of that color. We start by computing the frequencies of each value.  We then compute the cumulative frequency count.  After that we divide by the total count to get the cumulative probability distribution (we multiply by 255 so the values will be between 0 and 255).

 

To the right are the examples of what this process does to Lena.  The top is the histogram equilization to the blue component.  The middle picture is the green component and the last picutre is the red component.

 

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