中文说明：如果一副图像的像素占有很多的灰度级而且分布均匀，那么这样的图像往往有高对比度和多变的灰度色调。直方图均衡化就是一种能仅靠输入图像直方图信息自动达到这种效果的变换函数。它的基本思想是对图像中像素个数多的灰度级进行展宽，而对图像中像素个数少的灰度进行压缩，从而扩展像原取值的动态范围，提高了对比度和灰度色调的变化，使图像更加清晰。
English Description：
If a pair of images of the pixel occupies a lot of gray level and the distribution is even, then such images often have high contrast and variable gray tone. Histogram equalization is a kind of transformation function that can automatically achieve the effect of the input image histogram information. The basic idea is to broadening the gray level of the image pixels in a multiple, and the image pixels in a few gray compression, which extends as the dynamic range of the original value, improve the contrast and gray tone changes, make the image clearer.