What does imresizemex do in Matlab imresize function? - matlab

Question

I was trying to create an image resize code using C to do exactly what imresize.m in Matlab does. I stuck at the line calling imresizemex in imresize.m. It seems that imresizemex is a compiled machine code that can only be called in Matlab (I found it as imresizemex.mexw64 file in a Matlab private folder, no source code available). I also tried to call it in C, but failed. Does anyone know where to find the source code for imresizemex? Thanks a lot!

Answer 1

I think I figured it out ^ ^. It does the weighted multiplication and sum part of the cubic convolution interpolation. Here's my Matlab code replacing imresizemex. Although almost 6 seconds slower, it produces exactly the same result.
function outimg=reducesize(inimg, weights,indices,dim)
% reduce first dimension
reduce1=zeros(dim(1),size(inimg,2));
weight1=weights{1};
index1=indices{1};
for i=1:size(inimg,2)
for j=1:dim(1)
w11=weight1(j,:);
ind11=index1(j,:);
B=double(inimg(ind11,i));
v=w11.*B';
reduce1(j,i)=sum(v);
end
end
% reduce second dimension
reduce2=zeros(dim(1),dim(2));
weight2=weights{2};
index2=indices{2};
for i=1:dim(1)
for j=1:dim(2)
w22=weight2(j,:);
ind22=index2(j,:);
B=reduce1(i,ind22);
v=w22.*B;
reduce2(i,j)=sum(v);
end
end
outimg=round(reduce2);