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From: bill@bilver.uucp (Bill Vermillion)
Newsgroups: misc.consumers,sci.electronics
Subject: Re: Cable Competition at Last!
Keywords: Direct Broadcast Coming Soon
Message-ID: <1991Jan31.230256.20580@bilver.uucp>
Date: 31 Jan 91 23:02:56 GMT
References: <1991Jan25.140848.24260@kodak.kodak.com> <1991Jan25.165057.671@ux1.cso.uiuc.edu> <1991Jan28.150552.3082@news.larc.nasa.gov>
Distribution: na
Organization: W. J. Vermillion - Winter Park, FL
Lines: 35

In article <1991Jan28.150552.3082@news.larc.nasa.gov> kludge@grissom.larc.nasa.gov      ( Scott Dorsey) writes:
>In article <1991Jan25.165057.671@ux1.cso.uiuc.edu> mas35638@uxa.cso.uiuc.edu (Odin) writes:
>>> 480 lines
>>
>>525 is standard.  You're talking about a picture which is not as
>>good as normal tv broadcasts.
>
>Yes, but of those 525 lines, many of them carry vertical synch information.
>Most TV broadcasts use about 480 lines vertically.
>

Display lines DON'T equal resolution.  The 480 lines displayed will
give 240 lines resolution.  It takes two lines (or a pair) to
resolve 1 line.   THink of it this way.  If you had 480 horizontal
lines and put them on video, the screen would be all white or all
black as there is nothing to separate the lines.

TV pictures are 4 units wide and 3 units high.  Take the approx
240, and divided by 3 and multiply by 4.  You get 320.  That is the
horizontal resolution spec.  This gives approximately equal
horizontal and vertical resolution.

When you have a higher bandwidth, you can turn the horizontal trace
on and off faster.  Doing this increases the amount of vertical
line pairs you can display.   

There is a limit to the amount of apparent resolution you increase
because the resolution limit by the NUMBER of horizontal trace
lines will fool the brain so it won't see the resolution increased
by the number of TIMES the horizontal trace line is turned on/off.
(eg, how small the dots are going left to right).

-- 
Bill Vermillion - UUCP: uunet!tarpit!bilver!bill
                      : bill@bilver.UUCP


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