MadSci Network: Physics

Re: If a computer screen is shown on television, it appears to flicker. Why?

Date: Wed Jun 6 12:51:59 2001
Posted By: Michael L. Roginsky, Staff, Avionics, Honeywell Defense Avionics
Area of science: Physics
ID: 989249990.Ph

Hello Shubha: What you see in the flicker is called aliasing. This 
phenomenon is common to all sampling systems (non-continuous). The way 
pictures are displayed on the cathode ray tube (both computer and 
television) is by either a single beam (black and white) or triple 
red_blue_green beams (color) painting lines left to right and up to down 
at given time intervals. Some instances use "interlacing" meaning the 
lines are drawn with one-line gaps at a time and blank files filled-in 
before the next update. One thing is, if the scans and scan rates aren't 
synchronized the picture of the picture shows a lot of distortion to the 
point that information is indiscernible.
Aliasing is also evident in movies in the case of rotating spoke wheels. 
Depending on the velocity of the wheels, they sometimes reverse the 
Instrumentation engineers use sample data systems in many applications. To 
ensure validity of the data, either pre-sample filters or over-sampling 
speeds must be used.
Here are some Internet sites you may find helpful:
Your MAD.SCI Micro

Current Queue | Current Queue for Physics | Physics archives

Try the links in the MadSci Library for more information on Physics.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2001. All rights reserved.