[love801]

[M,N] = size(I1);  %返回矩阵的行数和列数 ，行数赋给M，列数赋给N
MSE1 = 0;
for i = 1:M
    for j = 1:N
        MSE1=MSE1+sum(sum((I1(i,j) - I2(i,j))*((I1(i,j) - I2(i,j)))));  %不懂这句的意思，I1,I2都是读入的图片数据，
   
    end
end