can anyone pls explain these lines????

filename=uigetfile('.jpg');
I=imread(filename);
I=imresize(I,[256 256]);
figure,imshow(I);
title('input image')

%----imnoise

I_n=I;

J=zeros(size(I_n));
for iclr=1:3
I_n = I(:,:,iclr);

[m n]=size(I_n);
BH=imhist(I_n);
[v p1]=max(BH);
pn=find(BH~=v);
[v p2]=max(BH(pn));
s_p=[p1-1 p2-1];
I_sp=zeros([m n]);
sp1=find(I_n==s_p(1));
I_sp(sp1)=1;
sp2=find(I_n==s_p(2));
I_sp(sp2)=1;

J(:,:,iclr)=I_n;
for i=2:m-1
    for j=2:n-1
        b_3=I_n(i-1:i+1,j-1:j+1);
        if I_sp(i,j)==1            
            J(i,j,iclr)=median(double(b_3(:)));
        end
    end
end

end

%-----filtered image

figure,imshow(uint8(J));

[Walter Roberson]

duplicates http://www.mathworks.co.uk/matlabcentral/answers/113748-i-am-new-to-matlab-can-anyone-please-explain-this-lines