Path: utzoo!utgpu!watmath!att!mtuxo!lzfme!ralph
From: ralph@lzfme.att.com (Ralph Brandi)
Newsgroups: comp.sys.mac
Subject: Re: Help Me! Mac II -> NTSC (repost)
Message-ID: <1567@lzfme.att.com>
Date: 17 Aug 89 12:51:47 GMT
References: <475@mit-amt.MEDIA.MIT.EDU>  <4568@uhccux.uhcc.hawaii.edu> <13545@bloom-beacon.MIT.EDU>
Reply-To: ralph@lzfme.att.com (Ralph Brandi)
Organization: AT&T Bell Labs, Commercial Art
Lines: 40

In article <13545@bloom-beacon.MIT.EDU> captkidd@athena.mit.edu (Ivan Cavero Belaunde) writes:
>In article <4568@uhccux.uhcc.hawaii.edu> bmartin@uhccux.UUCP (Brian Martin) writes:
>> The biggest
>>drawback when we tried it was that the menu bars and both right and
>>left sides of the screen were cut off--makes it difficult to
>>demonstrate a user-friendly system with pull-down menus, or to open
>>a disk partition on the right side of the screen. Also, there
>>was a very annoying flicker on screen. All in all, quite a let down.

>While I haven't seen this hack work, we have the same problems when we try
>to output NTSC video with our NuVista 2M board (overlaying video an
>graphics on the monitor is no problem - it is the NTSC [TV] output which
>flickers and loses the edges).  It is my understanding that this is a problem
>with NTSC video's limited bandwidth.


The flicker is a result of the fact that NTSC signals are interlaced; 
The complete frame is updated 30 times every second (29.97, if you
want to get really picky).  Each frame is made up of two fields.
And there's nothing you can do about it, except adapt your drawings
to the limitations of NTSC (f'rinstance, avoid horizontal single 
pixel lines, or even lines with an odd number of pixels as a width).

The edge problem is not strictly speaking an artifact of NTSC, but
rather of the way consumer TVs are made.  They use a technique
called overscan, so that the entire picture tube has a picture on
it.  This is supposedly more aesthetically pleasing for the general
public.  Computer monitors, on the other hand, are underscanned, so
you don't miss any information.  When I worked at a television
station as a camera operator, it was a rule of thumb to ignore the
outside 15 or 20% of the screen in composing our shots.  Some of us
even used a grease pencil to mark on our camera monitors what was
likely to be lost by the time the picture got to people's homes.

In other words, you just have to live with it.  Or wait for
HDTV....
-- 
Ralph Brandi    [most gateways in the known universe]!att!lzfme!ralph

Work flows toward the competent until they are submerged.