Well, I'm not 100% positive what BlitzMax does, but I think it adjusts the UV coordinates to fit. So you're not really scaling, but where those UV coordinates have been adjusted - and because of floating point inaccuracy - that UV coordinate is probably not exactly on a pixel border any more. So the scale is being very slightly offset, and I don't know if it will be enough to make a difference. But if it is ugly, you'll need to load the image with mip maps included.