1. Computer comprising: processor; computer readable storage medium accessible to the processor and bearing instructions executable by the processor to cause the processor to: receive an image; generate plural one-dimensional histograms using respective rows of pixel values in the image, the one-dimensional histograms being generated simultaneously in parallel with each other; generate a two-dimensional histogram using the one-dimensional histograms; determine at least one characteristic value of the two-dimensional histogram; and apply the characteristic value to the image to change at least one pixel value of the image.