timppu: Then you'd have to use two whitescreens for your projector, one 16:9 (for movies) and one 4:3 (for old games), and zoom it properly for each.
If you display a 4:3 picture on a 16:9 canvas, certainly there are empty (black) areas on the sides. Zooming the areas out won't help because then you'd also zoom the top and bottom of the image out of the screen.
SirPrimalform: Naturally, I was taking that as a given.
Any black that a projector shows will simply have the natural colour of the screen, and thus blend with the surroundings, meaning that a difference in aspect ratio will only be visible if you use a screen with borders.
You could display any shape on a black background, and the background would blend with the screen or wall - because the black simply isn't lit up by the projector, just like the rest of the wall.
Having a screen with borders looks really nice when it's set up correctly, but I regret getting such a screen because the projector is
very slightly off-centre, so it can't ever get aligned just right, and the height is always slightly off when I pull it down, so I have to fix that every damned time I'm probably also missing a few pixels in the corners where the picture goes outside the border.
A fully white one would have been a fuckload easier - set it up so it looks good enough, and bam, done. At least if you're content with not necessarily having the picture corners at exactly 90 degrees (you can get close, but you'll never get precisely there).
EDIT: Oh, sorry for the late reply, didn't notice the thread had been resurrected. Oh well, at least it was by the original poster.