说明：  直方图规定化，用于matlab图像处理。所谓直方图规定化，就是通过一个灰度映像函数，将原灰度直方图改造成所希望的直方图。所以，直方图修正的关键就是灰度映像函数。
(Histogram specification for matlab image processing. The so-called histogram specification is through a grayscale image function, the original histogram transformed into the desired histogram. Therefore, the key is the gray image histogram correction function.)