% downsample4.m

dat = imread('test_image.tif');
dat2 = dat(310:327,334:351,:);
clear dat;

[h,w,dummy] = size(dat2);
dat2 = double(dat2);

% reduce the data. Average 2x2 blocks
for lx=1:w/2,
for ly=1:h/2,
   x = (lx-1)*2+1;
   y = (ly-1)*2+1;
   dat_reduced(ly,lx,1) = (dat2(y,x,1) + dat2(y+1,x,1) + dat2(y,x+1,1) + dat2(y+1,x+1,1))/4;
   dat_reduced(ly,lx,2) = (dat2(y,x,2) + dat2(y+1,x,2) + dat2(y,x+1,2) + dat2(y+1,x+1,2))/4;
   dat_reduced(ly,lx,3) = (dat2(y,x,3) + dat2(y+1,x,3) + dat2(y,x+1,3) + dat2(y+1,x+1,3))/4;
end
end

% use interpolation methods to reconstruct an image
% of the original size

dat_reconstructed = zeros(h-1,w-1,3);

dat_reconstructed(:,:,1) = interp2([1:2:h],[1:2:w]',dat_reduced(:,:,1), [1:h-1],[1:w-1]','linear');
dat_reconstructed(:,:,2) = interp2([1:2:h],[1:2:w]',dat_reduced(:,:,2), [1:h-1],[1:w-1]','linear');
dat_reconstructed(:,:,3) = interp2([1:2:h],[1:2:w]',dat_reduced(:,:,3), [1:h-1],[1:w-1]','linear');
dat_reconstructed = uint8(dat_reconstructed);
figure();
image(dat_reconstructed);
title('linear interpolation');

dat_reconstructed(:,:,1) = interp2([1:2:h],[1:2:w]',dat_reduced(:,:,1), [1:h-1],[1:w-1]','spline');
dat_reconstructed(:,:,2) = interp2([1:2:h],[1:2:w]',dat_reduced(:,:,2), [1:h-1],[1:w-1]','spline');
dat_reconstructed(:,:,3) = interp2([1:2:h],[1:2:w]',dat_reduced(:,:,3), [1:h-1],[1:w-1]','spline');
dat_reconstructed = uint8(dat_reconstructed);
figure();
image(dat_reconstructed);
title('spline interpolation');