The trick with local contrast enhancement is that it increases “local” contrast in smaller regions, while at the same time preventing an increase in “global” contrast– thereby protecting large-scale shadow/highlight detail. It achieves this feat by making some pixels in the histogram cross over each other, which is not possible when enhancing contrast using levels or curves.
Local contrast enhancement works similarly to sharpening with an unsharp mask, however the mask is instead created using an image with a greater blur distance. This creates a local contrast mask which maps larger-scale transitions than the small-scale edges which are mapped when sharpening an image.
