You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: MSSIM.m
    path of file: ./repos/TIGRE/MATLAB/Utilities/Quality_measures
    
    the code of the file until where you have to start completion: function [simi]=MSSIM(real,res)
%Compute the mean structural similarity index to measure the similarity of
% two images in terms of luminance (l), contrast (c) and structure (s)that
% is designed to provide a good approximation of perceptual image quality
%
%
%--------------------------------------------------------------------------
%--------------------------------------------------------------------------
% This file is part of the TIGRE Toolbox
% 
% Copyright (c) 2015, University of Bath and 
%                     CERN-European Organization for Nuclear Research
%                     All rights reserved.
%
% License:            Open Source under BSD. 
%                     See the full license at
%                     https://github.com/CERN/TIGRE/blob/master/LICENSE
%
% Contact:            tigre.toolbox@gmail.com
% Codes:              https://github.com/CERN/TIGRE/
% Coded by:           Manasavee Lohvithee
%--------------------------------------------------------------------------

%real = exact phantom
%res = reconstructed image

    
function [simi]=MSSIM(real,res)
%Compute the mean structural similarity index to measure the similarity of
% two images in terms of luminance (l), contrast (c) and structure (s)that
% is designed to provide a good approximation of perceptual image quality
%
%
%--------------------------------------------------------------------------
%--------------------------------------------------------------------------
% This file is part of the TIGRE Toolbox
% 
% Copyright (c) 2015, University of Bath and 
%                     CERN-European Organization for Nuclear Research
%                     All rights reserved.
%
% License:            Open Source under BSD. 
%                     See the full license at
%                     https://github.com/CERN/TIGRE/blob/master/LICENSE
%
% Contact:            tigre.toolbox@gmail.com
% Codes:              https://github.com/CERN/TIGRE/
% Coded by:           Manasavee Lohvithee
%--------------------------------------------------------------------------

%real = exact phantom
%res = reconstructed image
real=real(:);
res=res(:);

N=length(real);

%compute the mean pixel values of the two images
meanreal=mean(real);
meanres=mean(res);


%Luminance comparison

K1=0.01; %K1 is a small constant <<1
d=max(real)-min(real); % d is the dynamic range of the pixel values. Check!

l=((2*meanreal*meanres)+(K1*d)^2)/((meanreal)^2+(meanres)^2+(K1*d)^2);

%Contrast comparison
K2=0.03;  %K2 is a small constant <<1
sreal=std(real);
sres=std(res);

c=((2*sreal*sres)+(K2*d)^2)/((sreal)^2+(sres)^2+(K2*d)^2);

%Structure comparison

diffreal=real-meanreal;
diffres=res-meanres;

delta=(1/(N-1))*sum(diffreal.*diffres);

s=(delta+(((K2*d)^2)/2))/((sreal*sres)+(((K2*d)^2)/2));


%Calculate MSSIM
simi=(1/N)*sum(l*c*s);

end