ssim_index

PURPOSE ^

SYNOPSIS ^

function [mssim, ssim_map] = ssim_index(img1, img2, K, window, L)

DESCRIPTION ^

CROSS-REFERENCE INFORMATION ^

This function calls: This function is called by:

SOURCE CODE ^

0001 
0002 function [mssim, ssim_map] = ssim_index(img1, img2, K, window, L)
0003 
0004 if (nargin < 2 | nargin > 5)
0005    ssim_index = -Inf;
0006    ssim_map = -Inf;
0007    return;
0008 end
0009 
0010 if (size(img1) ~= size(img2))
0011    ssim_index = -Inf;
0012    ssim_map = -Inf;
0013    return;
0014 end
0015 
0016 [M N] = size(img1);
0017 
0018 if (nargin == 2)
0019    if ((M < 11) | (N < 11))
0020        ssim_index = -Inf;
0021        ssim_map = -Inf;
0022       return
0023    end
0024    window = fspecial('gaussian', 11, 1.5);
0025    K(1) = 0.01;
0026    K(2) = 0.03;
0027    L = 255;
0028 end
0029 
0030 if (nargin == 3)
0031    if ((M < 11) | (N < 11))
0032        ssim_index = -Inf;
0033        ssim_map = -Inf;
0034       return
0035    end
0036    window = fspecial('gaussian', 11, 1.5);
0037    L = 255;
0038    if (length(K) == 2)
0039       if (K(1) < 0 | K(2) < 0)
0040            ssim_index = -Inf;
0041            ssim_map = -Inf;
0042            return;
0043       end
0044    else
0045        ssim_index = -Inf;
0046        ssim_map = -Inf;
0047        return;
0048    end
0049 end
0050 
0051 if (nargin == 4)
0052    [H W] = size(window);
0053    if ((H*W) < 4 | (H > M) | (W > N))
0054        ssim_index = -Inf;
0055        ssim_map = -Inf;
0056       return
0057    end
0058    L = 255;
0059    if (length(K) == 2)
0060       if (K(1) < 0 | K(2) < 0)
0061            ssim_index = -Inf;
0062            ssim_map = -Inf;
0063            return;
0064       end
0065    else
0066        ssim_index = -Inf;
0067        ssim_map = -Inf;
0068        return;
0069    end
0070 end
0071 
0072 if (nargin == 5)
0073    [H W] = size(window);
0074    if ((H*W) < 4 | (H > M) | (W > N))
0075        ssim_index = -Inf;
0076        ssim_map = -Inf;
0077       return
0078    end
0079    if (length(K) == 2)
0080       if (K(1) < 0 | K(2) < 0)
0081            ssim_index = -Inf;
0082            ssim_map = -Inf;
0083            return;
0084       end
0085    else
0086        ssim_index = -Inf;
0087        ssim_map = -Inf;
0088        return;
0089    end
0090 end
0091 
0092 C1 = (K(1)*L)^2;
0093 C2 = (K(2)*L)^2;
0094 window = window/sum(sum(window));
0095 img1 = double(img1);
0096 img2 = double(img2);
0097 
0098 mu1   = filter2(window, img1, 'valid');
0099 mu2   = filter2(window, img2, 'valid');
0100 mu1_sq = mu1.*mu1;
0101 mu2_sq = mu2.*mu2;
0102 mu1_mu2 = mu1.*mu2;
0103 sigma1_sq = filter2(window, img1.*img1, 'valid') - mu1_sq;
0104 sigma2_sq = filter2(window, img2.*img2, 'valid') - mu2_sq;
0105 sigma12 = filter2(window, img1.*img2, 'valid') - mu1_mu2;
0106 
0107 if (C1 > 0 & C2 > 0)
0108    ssim_map = ((2*mu1_mu2 + C1).*(2*sigma12 + C2))./((mu1_sq + mu2_sq + C1).*(sigma1_sq + sigma2_sq + C2));
0109 else
0110    numerator1 = 2*mu1_mu2 + C1;
0111    numerator2 = 2*sigma12 + C2;
0112     denominator1 = mu1_sq + mu2_sq + C1;
0113    denominator2 = sigma1_sq + sigma2_sq + C2;
0114    ssim_map = ones(size(mu1));
0115    index = (denominator1.*denominator2 > 0);
0116    ssim_map(index) = (numerator1(index).*numerator2(index))./(denominator1(index).*denominator2(index));
0117    index = (denominator1 ~= 0) & (denominator2 == 0);
0118    ssim_map(index) = numerator1(index)./denominator1(index);
0119 end
0120 
0121 mssim = mean2(ssim_map);
0122 
0123 return

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