% downsample.m

dat = imread('test_image.tif');
dat2 = dat(310:326,334:350,:);
clear dat;

figure();
image(dat2);
title('original')

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

for lx=1:w/2,
for ly=1:h/2,
   x = (lx-1)*2+1;
   y = (ly-1)*2+1;
   mr = (dat2(y,x,1) + dat2(y+1,x,1) + dat2(y,x+1,1) + dat2(y+1,x+1,1))/4;
   mg = (dat2(y,x,2) + dat2(y+1,x,2) + dat2(y,x+1,2) + dat2(y+1,x+1,2))/4;
   mb = (dat2(y,x,3) + dat2(y+1,x,3) + dat2(y,x+1,3) + dat2(y+1,x+1,3))/4;
   dat3(y:y+1,x:x+1,1) = mr;
   dat3(y:y+1,x:x+1,2) = mg;
   dat3(y:y+1,x:x+1,3) = mb;
end;
end;
figure();
dat3 = uint8(dat3);
image(dat3);
title('down-sampled');