upsample.m

%{
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% Upsampling procedure.
%
% Argments:
%   'I': greyscale image
%   'odd': 2-vector of binary values, indicates whether the upsampled image
%   should have odd size for the respective dimensions
%   'filter': upsampling filter
%
% If image width W is odd, then the resulting image will have width (W-1)/2+1,
% Same for height.
%
% tom.mertens@gmail.com, August 2007
%

function R = upsample(I,odd,filter)

% increase resolution
I = padarray(I,[1 1 0],'replicate'); % pad the image with a 1-pixel border
r = 2*size(I,1);
c = 2*size(I,2);
k = size(I,3);
R = zeros(r,c,k);
R(1:2:r, 1:2:c, :) = 4*I; % increase size 2 times; the padding is now 2 pixels wide

% interpolate, convolve with separable filter
R = imfilter(R,filter);     %horizontal
R = imfilter(R,filter');    %vertical

% remove the border
R = R(3:r - 2 - odd(1), 3:c - 2 - odd(2), :);