Actually the minimum number of pixels to render a close box is three times the number of close boxes (ie. 3x3 for 1 close box). Any fewer pixels will not allow

Actually the minimum number of pixels to render a close box is three times the number of close boxes (ie. 3x3 for 1 close box). Any fewer pixels will not allow a functional close box to be reconstructed. This is referered to as the 'Nah-quist limit'.