说明：  本程序主要用两种方法对前后输入两幅RGB图像计算处理，分别计算了其均方差MSE和峰值信噪比PSNR；方法1:如果读入图像为彩色图象, 首先进行灰度化处理,依照灰度图象计算 方法2:对RGB图像均方差是所有方差之和除以图像尺寸再除以3
(This program before and after the input of two ways two RGB image calculation process to calculate the mean square error MSE and PSNR PSNR Method 1: If you read into the image as a color image, the first gray-scale processing Method 2: RGB image variance calculated in accordance with the gray-scale image is all variance divided by image size divided by 3)