请写出输入两张图片，计算出这两张图片的SSIM的matlab完整代码（不用matlab内置函数，不适用cov）

以下是计算两张图片的SSIM的Matlab代码：

% 读入两张图像
img1 = imread('image1.jpg');
img2 = imread('image2.jpg');

% 转换为double类型
img1 = im2double(img1);
img2 = im2double(img2);

% 常量设置
K1 = 0.01;
K2 = 0.03;
L = 1;
window = fspecial('gaussian', 11, 1.5);

% 计算均值，标准差和协方差
mu1 = filter2(window, img1, 'valid');
mu2 = filter2(window, img2, 'valid');
mu1_sq = mu1.^2;
mu2_sq = mu2.^2;
mu1_mu2 = mu1.*mu2;

sigma1_sq = filter2(window, img1.^2, 'valid') - mu1_sq;
sigma2_sq = filter2(window, img2.^2, 'valid') - mu2_sq;
sigma12 = filter2(window, img1.*img2, 'valid') - mu1_mu2;

% 计算SSIM指数
numerator = (2*mu1_mu2 + K1)*(2*sigma12 + K2);
denominator = (mu1_sq + mu2_sq + K1)*(sigma1_sq + sigma2_sq + K2);
ssim_map = numerator./denominator;

% 计算平均SSIM指数
ssim_index = mean2(ssim_map);

% 显示结果
fprintf('The SSIM index between the two images is %0.4f.\n', ssim_index);

注意，这里使用了一个高斯窗口来平滑图像。可以根据需要调整窗口大小和标准差。