Contrast enhancement, as described in the previous section, yields an image having a full range of intensities. However, highlights and shadows are blocked out. As long as we reallocate light levels on a {\em global} basis, what is an optimal reallocation for one area may not be optimal for another area---and there are not enough levels in the final medium to satisfy everybody at the same time.

Contrast enhancement on a global basis

Postscript Version