Originally Posted by pixelation
Assuming the projector outputs at 16:9 1080p, isn't it easier to just move the projector back, make it brighter and use 2 pieces of paper to block off the light above and below?
Not really, first, you can't always move it back.
Second, moving it back makes the picture dimmer, about 44%.
You can't always make it brighter, and doing so generally has consequences from higher noise level (high lamp verses low/eco) to reduced contrast.
And lastly, there's no place between the projector and the screen (other than very near the screen) that's within the focal plane, so anything used to block light would result in a very blurry edge, not a sharp one. The only two places you can achieve sharp masked edges are at the screen, and directly at the imaging device inside the projector.