??? Error using ==> times Matrix dimensions must agree

I'm trying to process image using this ssim coding but i found that this error appear. I don't know where the error is. Can help me ? tq.

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

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
img1 = double(img1);
img2 = double(img2);
% automatic downsampling
f = max(1,round(min(M,N)/256));
%downsampling by f
%use a simple low-pass filter 
if(f>1)
    lpf = ones(f,f);
    lpf = lpf/sum(lpf(:));
    img1 = imfilter(img1,lpf,'symmetric','same');
    img2 = imfilter(img2,lpf,'symmetric','same');
      img1 = img1(1:f:end,1:f:end);
      img2 = img2(1:f:end,1:f:end);
  end
C1 = (K(1)*L)^2;
C2 = (K(2)*L)^2;
window = window/sum(sum(window));
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

[Walter Roberson]

As we do not have your input data, we don't know where the error is either.

You could help by indicating the exact line the error occurs on.

Have you tried using the debugger to figure out what the matrix sizes _are_ at the time?

Answer 1

[per isakson]

See the page "Avoid Mistakes While Editing Code" in the documentation.

The Code Analyzer of the Matlab Editor works in the background and displays a summary in the Message Indicator in upper right corner of the editor pane. It works a bit like the spell checker in a word processor. Try to keep the Message Indicator green and understand that if it is red you have a problem.

Anyhow, there is syntax error in the following line

    ssim_map = ((2*mu1_mu2) + C1).* ........

I fixed that and run your code with two versions of moon.tif. The function returned a meaningful result.

--- EDIT ---

The two first input arguments must have the same size. However, your code doesn't test that.

    >> [mssim, ssim_map] = ssim(moon1,moon2(:,1:end-1));
    Error using  .* 
    Matrix dimensions must agree.
    Error in ssim (line 105)
        mu1_mu2 = (mu1.*mu2);