Histogram shows the statistic relation between every gray level and the probability of its occurrence

giving the global information of the image. Gray scale transformation based on the technique of histogram modification is one of practical and effective ways of image enhancement. Histogram processing includes equalization and specification. The aim of equalization is to create an image with equally distributed brightness levels over the whole brightness scale; The aim of specification is to transform the histogram of an original image to a specified histogram capable of highlighting certain gray level ranges in the image. In order to improve the efficiency of the algorithm of histogram processing further

the shortcomings of several current algorithms of equalization transformation and specification transformation are first analyzed

then a new binary mapping law (BML) is proposed. That law is based on optimal control theory making gray scale mapping abide by the principle of the minimum error of histogram

and haves a simple algorithm. Whether for histogram equalization or for histogram specification

it is testified more efficient than other mapping laws.