??? Keystone correction permits the sides of the image to be slanted (and the top of
the image to be made smaller than the bottom, or vice versa) so that the image
will appear rectangular when projected onto the screen at an angle.
??? Image scaling and multiple video inputs enable a clear picture to be projected
despite huge variations in the resolution, quality, and speed of the incoming
signals.
Video timing
When dealing with video signals, timing is everything. In order to display a stable
picture and accurately locate each dot during the scanning process, the timing of the
video signal must be very precise.
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16 Chapter 1: Introduction to the X Window System
The speed of the video signal is dictated by the screen resolution and refresh (scan)
rate. Resolution is defined in terms of horizontal and vertical pixels; scan rate is
expressed in Hertz (Hz), or cycles per second. A scan rate of 70 Hz or higher is recommended
for CRTs in order to reduce eyestrain for the user; the refresh rate is not
as important for most LCD displays, because the decay time (the time it takes a pixel
to change color) is longer.
The length of cable that may be used to connect a video monitor to a video card is
directly limited by the scan rate.
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