clc;

close all;

X = imread('q1.tif');%             读取图像

Y=imread('q2.tif');

figure;%                           展示图像

subplot(1, 3, 1); imshow(X); title('q1');

subplot(1, 3, 2); imshow(Y); title('q2');

%                                  使得图像每个像素值为浮点型

X = double(X);

Y = double(Y); 

A = Y-X;

B = X.*Y;

subplot(1,3,3);imshow(A);title('作差');

MSE = sum(A(:).*A(:))/numel(Y);%  均方根误差MSE，numel()函数返回矩阵元素个数

SNR = 10*log10(sum(X(:).*X(:))/MSE/numel(Y));%信噪比SNR

PSNR = 10*log10(255^2/MSE);%      峰值信噪比PSNR

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%以下为结构相似度SSIM

ux=sum(X(:).*X(:))/numel(X);

uy=sum(Y(:).*Y(:))/numel(Y);

sigmoidx=sum(X(:).*X(:)-ux)/numel(X);

sigmoidy=sum(Y(:).*Y(:)-uy)/numel(Y);

sigmoidxy=sum(B(:).*B(:))/(numel(B)*ux*uy)-ux*uy;

SSIM=(2*ux*uy)*(2*sigmoidxy)/(ux*ux+uy*uy)/(sigmoidx*sigmoidx+sigmoidy*sigmoidy);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

display(MSE);%均方根误差MSE

display(SNR);%信噪比SNR

display(PSNR);%峰值信噪比PSNR

display(SSIM);%结构相似性SSIM

MSE =153.6263

SNR =19.7617

PSNR =26.2661

SSIM =-1.5281e+26