Re: Computer Flickering

["Arlen P. Walker" <Arlen -dot- P -dot- Walker -at- JCI -dot- COM>]

     Is this why computer screens always "flicker" on TV?

In a way. In that case the scan rate of the TV (30 Hz) is far enough off the
scan rate of the monitor that imcomplete scans of the monitor are caught on
camera.

More than you wanted to know about CRT operation:

The pixels on the screen are excited one at a time by an electron gun (three --
one each for R, G, B -- in all but Sony color monitors, but the actual number is
immaterial) when the pixel is excited it glows brightly, and as soon as the gun
passes on to the next pixel, it begins to dim. The rate at which it is excited
is the refresh rate (30Hz, 65Hz, 72Hz, or whatever).

A TV camera picks up the state of the entire screenful of pixels at an instant
in time. Some will be bright (having been most recently excited) and some will
be noticeably dimmer (having been least recently excited). If the refresh rate
of the monitor is not an exact multiple of the camera's rate of capturing the
screens then a different area of the screen will be bright in each succeeding
video or film frame. This makes the monitor's image seem to flicker.

Funny. Explaining things to accountants, marketing folks, even VP's doesn't make
me nervous. Posting an explanation of something technical here does. ;{>}


Have fun,
Arlen
Chief Managing Director In Charge, Department of Redundancy Department
DNRC 24

Arlen -dot- P -dot- Walker -at- JCI -dot- Com
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