说明：  用matlab函数imhist()实现给定图像的直方图；函数histeq()实现直方图均衡化；对给定图像，各自指定直方图，进行直方图匹配，使图像增强。
(Using matlab function imhist () to achieve a given image histogram function histeq () to achieve histogram equalization on a given image, each designated histogram, histogram matching, so that the image enhancement.)