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Diffstat (limited to 'supp/ssim_index.m')
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diff --git a/supp/ssim_index.m b/supp/ssim_index.m new file mode 100644 index 0000000..4fa7a79 --- /dev/null +++ b/supp/ssim_index.m @@ -0,0 +1,181 @@ +function [mssim, ssim_map] = ssim_index(img1, img2, K, window, L) + +%======================================================================== +%SSIM Index, Version 1.0 +%Copyright(c) 2003 Zhou Wang +%All Rights Reserved. +% +%This is an implementation of the algorithm for calculating the +%Structural SIMilarity (SSIM) index between two images. Please refer +%to the following paper: +% +%Z. Wang, A. C. Bovik, H. R. Sheikh, and E. P. Simoncelli, "Image +%quality assessment: From error visibility to structural similarity" +%IEEE Transactios on Image Processing, vol. 13, no. 4, pp.600-612, +%Apr. 2004. +% +%Kindly report any suggestions or corrections to zhouwang@ieee.org +% +%---------------------------------------------------------------------- +% +%Input : (1) img1: the first image being compared +% (2) img2: the second image being compared +% (3) K: constants in the SSIM index formula (see the above +% reference). defualt value: K = [0.01 0.03] +% (4) window: local window for statistics (see the above +% reference). default widnow is Gaussian given by +% window = fspecial('gaussian', 11, 1.5); +% (5) L: dynamic range of the images. default: L = 255 +% +%Output: (1) mssim: the mean SSIM index value between 2 images. +% If one of the images being compared is regarded as +% perfect quality, then mssim can be considered as the +% quality measure of the other image. +% If img1 = img2, then mssim = 1. +% (2) ssim_map: the SSIM index map of the test image. The map +% has a smaller size than the input images. The actual size: +% size(img1) - size(window) + 1. +% +%Default Usage: +% Given 2 test images img1 and img2, whose dynamic range is 0-255 +% +% [mssim ssim_map] = ssim_index(img1, img2); +% +%Advanced Usage: +% User defined parameters. For example +% +% K = [0.05 0.05]; +% window = ones(8); +% L = 100; +% [mssim ssim_map] = ssim_index(img1, img2, K, window, L); +% +%See the results: +% +% mssim %Gives the mssim value +% imshow(max(0, ssim_map).^4) %Shows the SSIM index map +% +%======================================================================== + + +if (nargin < 2 | nargin > 5) + ssim_index = -Inf; + ssim_map = -Inf; + return; +end + +if (size(img1) ~= size(img2)) + ssim_index = -Inf; + ssim_map = -Inf; + return; +end + +[M N] = size(img1); + +if (nargin == 2) + if ((M < 11) | (N < 11)) % ͼССû塣 + ssim_index = -Inf; + ssim_map = -Inf; + return + end + window = fspecial('gaussian', 11, 1.5); % һƫ1.511*11ĸ˹ͨ˲ + K(1) = 0.01; % default settings + K(2) = 0.03; % + L = 255; % +end + +if (nargin == 3) + if ((M < 11) | (N < 11)) + ssim_index = -Inf; + ssim_map = -Inf; + return + end + window = fspecial('gaussian', 11, 1.5); + L = 255; + if (length(K) == 2) + if (K(1) < 0 | K(2) < 0) + ssim_index = -Inf; + ssim_map = -Inf; + return; + end + else + ssim_index = -Inf; + ssim_map = -Inf; + return; + end +end + +if (nargin == 4) + [H W] = size(window); + if ((H*W) < 4 | (H > M) | (W > N)) + ssim_index = -Inf; + ssim_map = -Inf; + return + end + L = 255; + if (length(K) == 2) + if (K(1) < 0 | K(2) < 0) + ssim_index = -Inf; + ssim_map = -Inf; + return; + end + else + ssim_index = -Inf; + ssim_map = -Inf; + return; + end +end + +if (nargin == 5) + [H W] = size(window); + if ((H*W) < 4 | (H > M) | (W > N)) + ssim_index = -Inf; + ssim_map = -Inf; + return + end + if (length(K) == 2) + if (K(1) < 0 | K(2) < 0) + ssim_index = -Inf; + ssim_map = -Inf; + return; + end + else + ssim_index = -Inf; + ssim_map = -Inf; + return; + end +end +%% +C1 = (K(1)*L)^2; % C1Lxyá +C2 = (K(2)*L)^2; % C2ԱȶCxyá +window = window/sum(sum(window)); %˲һ +img1 = double(img1); +img2 = double(img2); + +mu1 = filter2(window, img1, 'valid'); % ͼ˲ӼȨ +mu2 = filter2(window, img2, 'valid'); % ͼ˲ӼȨ + +mu1_sq = mu1.*mu1; % Uxƽֵ +mu2_sq = mu2.*mu2; % Uyƽֵ +mu1_mu2 = mu1.*mu2; % Ux*Uyֵ + +sigma1_sq = filter2(window, img1.*img1, 'valid') - mu1_sq; % sigmax +sigma2_sq = filter2(window, img2.*img2, 'valid') - mu2_sq; % sigmay +sigma12 = filter2(window, img1.*img2, 'valid') - mu1_mu2; % sigmaxy + +if (C1 > 0 & C2 > 0) + ssim_map = ((2*mu1_mu2 + C1).*(2*sigma12 + C2))./((mu1_sq + mu2_sq + C1).*(sigma1_sq + sigma2_sq + C2)); +else + numerator1 = 2*mu1_mu2 + C1; + numerator2 = 2*sigma12 + C2; + denominator1 = mu1_sq + mu2_sq + C1; + denominator2 = sigma1_sq + sigma2_sq + C2; + ssim_map = ones(size(mu1)); + index = (denominator1.*denominator2 > 0); + ssim_map(index) = (numerator1(index).*numerator2(index))./(denominator1(index).*denominator2(index)); + index = (denominator1 ~= 0) & (denominator2 == 0); + ssim_map(index) = numerator1(index)./denominator1(index); +end + +mssim = mean2(ssim_map); + +return
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