中文说明：代码实现了两个功能，首先对图像画出直方图，然后对图像进行直方图均衡。为了突出均衡后图像的极大值与极小值部分，做了一个带通滤波功能，将极值周围的像素点变成极值，非极值周围的像素保持原来的大小。得到的图像就比较平滑。
English Description：
Code to achieve two functions, first draw the image histogram, and then histogram equalization of the image. In order to highlight the maximum and minimum parts of the balanced image, a band-pass filtering function is made, which turns the pixels around the extremum into extremum, and keeps the original size of the pixels around the non extremum. The resulting image is smoother.