Tim Kerby <PICLIST@MITVMA.MIT.EDU> wrote:

> The television uses a refresh of 25 frames per second.  Does your tv
> flicker?

Tim:

As you say, televisions (in countries with 50 Hz systems) refresh
the entire frame 25 times per second.  They do it, however, by
interlacing the odd and even lines (the odd and even "fields") and
refreshing each field FIFTY times per second.  This interlacing
scheme was adopted specifically to combat flicker.

Additionally, TV screens have much higher persistence than LEDs. That
is, once an image is drawn on a TV screen, it takes a while for it to
fade.  LEDs, on the other hand, have essentially zero persistence.

Finally, most people watch TV in fairly dim ambient light.  This
helps to reduce apparent flicker as well.

Even so, however, televisions DO flicker; a regular (60 Hz in the
USA) television looks absolutely AWFUL when it's compared
side-by-side to a frequency-doubled 120-Hz TV with a non-interlaced
display fed from a big RAM.

-Andy

=== Andrew Warren - fastfwd@ix.netcom.com                 ===
=== Fast Forward Engineering - Vista, California          ===
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