there are several ways to scale an image onscreen
almost all of the time using larger images - people want the image to scale smoothly - so it looks good at zoomed in resolutions - the pixels are interpolated--
when using low resolution images with exact sizes - the opposite is required - no interpolation
visfx2 -unity scale preserves image size and does not interpolate - when used in flat constant aspect ratio mixes.
visfx8 - turns off image interpolation and so exact pixels are displayed.