Video and displays
Keystone correction
A digital fix that squares up a trapezoid-shaped image caused by a tilted projector, at the cost of resolution and sharpness.
When a projector is aimed up or down at the screen, the image becomes a trapezoid because one edge is farther from the lens. Keystone correction pre-distorts the picture the opposite way so the result looks rectangular.
The correction rescales the image on the chip, so part of the panel goes unused and the rest is resampled. The result is a softer picture, scaling artifacts on fine text, and sometimes extra input lag. It is a convenience, not a substitute for correct mounting.
Aim for zero keystone in a permanent install and use lens shift or mounting height instead. If you must, keep it under about 10 degrees; at 15 degrees or more the loss of resolution is obvious on a 4K image.
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