comparison util/ssim_index.m @ 38:84b7c44e54c4

(none)

+function [mssim, ssim_map] = ssim_index(img1, img2, K, window, L)
+
+%========================================================================
+%SSIM Index, Version 1.0
+%Copyright(c) 2003 Zhou Wang
+%All Rights Reserved.
+%
+%The author is with Howard Hughes Medical Institute, and Laboratory
+%for Computational Vision at Center for Neural Science and Courant
+%Institute of Mathematical Sciences, New York University.
+%
+%----------------------------------------------------------------------
+%Permission to use, copy, or modify this software and its documentation
+%for educational and research purposes only and without fee is hereby
+%granted, provided that this copyright notice and the original authors'
+%names appear on all copies and supporting documentation. This program
+%shall not be used, rewritten, or adapted as the basis of a commercial
+%software or hardware product without first obtaining permission of the
+%authors. The authors make no representations about the suitability of
+%this software for any purpose. It is provided "as is" without express
+%or implied warranty.
+%----------------------------------------------------------------------
+%
+%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 measurement to structural similarity"
+%IEEE Transactios on Image Processing, vol. 13, no. 1, Jan. 2004.
+%
+%Kindly report any suggestions or corrections to [e-mail]
+%
+%----------------------------------------------------------------------
+%
+%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))
+	   ssim_index = -Inf;
+	   ssim_map = -Inf;
+      return
+   end
+   window = fspecial('gaussian', 11, 1.5);	%
+   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;
+C2 = (K(2)*L)^2;
+window = window/sum(sum(window));
+img1 = double(img1);
+img2 = double(img2);
+
+mu1   = filter2(window, img1, 'valid');
+mu2   = filter2(window, img2, 'valid');
+mu1_sq = mu1.*mu1;
+mu2_sq = mu2.*mu2;
+mu1_mu2 = mu1.*mu2;
+sigma1_sq = filter2(window, img1.*img1, 'valid') - mu1_sq;
+sigma2_sq = filter2(window, img2.*img2, 'valid') - mu2_sq;
+sigma12 = filter2(window, img1.*img2, 'valid') - mu1_mu2;
+
+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