Oh, it's a bug that happens when you use only black and white images! (try the example from "GrabImage" in the docs). If you scale a black and white image it sucks, probably because it uses 1 bit color or something...
The scaling looks actually very good if you use different colors ((255,255,254) is sufficient to make it work properly)
The scaling looks actually very good if you use different colors ((255,255,254) is sufficient to make it work properly)