Here's a gnarly one-liner to produce a checkerboard image ch with the same dimensions as you image im in matlab:
ch = repmat(1-0.2*xor((mod(repmat(0:size(im,2)-1,size(im,1),1),8*2)>7),(mod(repmat((0:size(im,1)-1)',1,size(im,2)),8*2)>7)),[1 1 3]);
This is useful for alpha-compositing. So suppose you had an alpha-map A to extract the star from this colorful image im. Then you could composite the star over ch:
imshow([ ...
ch; ...
repmat(A,[1 1 3]); ...
im; ...
bsxfun(@times,ch,1-A)+bsxfun(@times,im,A)])
Update: Here's an even gnarlier anonymous function which takes an image im and an alpha map A and produces an image of the composite over the checkboard:
checker = @(im,A) bsxfun(@times,1-A,repmat(1-0.2xor((mod(repmat(0:size(im,2)-1,size(im,1),1),82)>7),(mod(repmat((0:size(im,1)-1)',1,size(im,2)),8*2)>7)),[1 1 3])) + bsxfun(@times,A,im);
Then you can quickly display your checkboard background images with:
imshow(checker(im,A))
