包括画单图的直方图，均衡直方图，归一化直方图以及两幅图像的联合直方图；修正了读入图像时要在同一目录下、以及图像的格式和是否为RGB图像的限制；修正了画两幅图像联合直方图时，大小需要保持一致的限制-Paintings include single graph histogram, histogram equalization, the normalized image histogram and two joint histogram amended to read into the image