Take the Gimp in example when you magnify a picture, the considered squares representing pixels works like the green which would be 10 x 2 or blue 5 x 1.
As far i remember, the Degas Elite in 1987 which was working on Atari ST was also using this way of counting, so i think it would be the most natural way as this entered in people's habits...this is only my opinion it doesn't mean it must be like that
