Video Frame rates
//// Mike Fulton <75300.1141@compuserve.com> shares his views on
video frame rates:
[] The frame rate at which a game updates its screen doesn't
necessarily correspond in a particular way to the television or
monitor's frame rate. In fact, ideally the game's screen refresh
_should not_ be tied to the television's frame rate, because
otherwise the game plays differently on different types of TV sets.
And a TV really does do 60 frames per second, although a broadcast
TV signal is only 30 frames per second. Televisions use a method
called interlacing to increase the apparent vertical resolution of
the image. The electron gun of a picture tube paints the display
60 times per second, but it can only display about 262 lines of
vertical resolution in each frame, which isn't really very good. A
broadcast TV signal wants to have about 525 lines of vertical
resolution, so what they do is have the signal show only 30 frames
per second, but each frame is broken down into two 'fields'. One
field contains all the odd-numbered scanlines for a frame, and the
next field contains all the even-numbered scanlines. Each field is
displayed in one of the picture tube's 60hz frames, and the result
is that the eye sees a higher resolution picture than you'd
otherwise get.
Interlacing is a tricky thing, however, and if you have significant
differences in brightness or color between one scanline and the
next in the same frame, you get a flickering effect on screen
because the same part of the screen is changing back and forth 60
times per second. You don't notice this much in regular TV stuff
because they use tricks like anti-aliasing to get around it.
However you do see it in some instances, like in the overlay
lettering for some mail or phone-order commercials.
So while a regular broadcast TV signal is only 30 distinct images
per second, each image is actually using 2 frames of the picture
tube. I don't know for sure if this works on a TV, but I suspect
that if you don't interlace your signal this way, and settle for
lower resolution, you can get the full 60 frames per second.
I don't know what the actual frame rate of Wolfenstein 3D on the
Jaguar is, but I do know they had to slow it down to keep you from
running into the walls. We got a new, higher-resolution version
today and it's looking pretty good. You also have to consider that
the Jaguar can connect to higher quality monitors as well as
televisions.
PROWLER The Atari Console Disk Magazine February 27, 1996
Copyright (c) 1996 All Rights Reserved Issue No. 01