Having one for loop instead of two

I am trying to hardcode the upsampling of an image. The problem I am having is trying to do it in a loop. It seems impossible.Here is what I did.

Image = imread('grayscale.jpg');
%imshow(Image);
% Downsampling
[row, col] = size(Image);
Downimage = Image(1:2:row,1:2:col);
%imshow(Downimage);
%Upsampling
newrow = row*2;
newcol = col*2;
Upimage = zeros(newrow,newcol);
for r = 1:2:newrow
  for c = 1:2:newcol
    Upimage(r,c) = Downimage;              %The Downimage should also have different parameters but I cant just use r and c since their length are not the same
    Upimage(r+1,c+1) = Downimage;
  end
end
%Upimage = reshape([Downimage ; Downimage],1,[]);
%Upimage = repmat(Downimage, 2, 1);
imshow(Upimage);

Now I realize that for the loop to work it needs parameters beside the Downimage in the loop, but I can's seem to make it work due to the downimage being of the shorter size then the upimage. P.S I cant use imresize...I have to hardcode it

Answer 1

[Guillaume]

I'm not sure I understand your problem:

Upimage(r, c) = Downimage(ceil(r/2), ceil(c/2));
Upimage(r+1, c) = Downimage(ceil(r/2), ceil(c/2)); %or = Upimage(r, c)
%same for (r, c+1)
%same for (r+1, c+1)

would work. The four lines can simply be written as

Upimage(r:r+1, c:c+1) = Downimage(ceil(r/2), ceil(c/2));

[Guillaume]

Note that I would have had the loop going over the pixels of the DownImage rather than the UpImage. It makes for a simpler code:

for c = 1:col         %note that it is also faster to iterate over columns in the outer loop
  for r = 1:row
      UpImage(2*r-1:2*r, 2*c-1:2*c) = DownImage(r,c);
  end
end