pro  write_block, image, i, j, block, SIDE=side

;   side of a square block
if not(keyword_set(side)) then  side = 32


;   writting of the block
;   if block is a scalar, block will be a  side x side  constant array 
image[side*i:side*(i+1)-1, side*j:side*(j+1)-1] = block


return
end