NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/comp/multimed/3453

Internet Message Format | 1992-11-19 | 2.1 KB

Path: sparky!uunet!zaphod.mps.ohio-state.edu!darwin.sura.net!wupost!waikato.ac.nz!ldo
From: [e-mail] (Lawrence D'Oliveiro, Waikato University)
Newsgroups: comp.multimedia
Subject: Re: TV resolution?
Message-ID: <[e-mail]>
Date: 20 Nov 92 16:55:47 +1300
References: <[e-mail]> <[e-mail]> <[e-mail]> <[e-mail]> <[e-mail]>
Organization: University of Waikato, Hamilton, New Zealand
Lines: 31

In article <[e-mail]>, [e-mail]
(Robert J Woodhead) asks:
>
> exactly how is a line of resolution defined?
> Consider an alternating pattern of 640 white and dark lines (320 white,
> 320 dark) that my computer is displaying on a TV set.  I look closely and
> can see all of the white and dark lines (they don't merge).
>
> Am I seeing 640 lines of resolution, or only 320?  By the above description
> (since it says 500 lines vertical, and there are only 525 scan lines to
> begin with), I'd assume I'm seeing 640, but inquiring minds want to know.

The problem is that some people are confusing a digital measure of resolution
with an analog one.

In analog terms, an image in the form of a repeating pattern (such as those
alternating lines) translates into a waveform with a specific frequency in the
video signal. In trying to represent this waveform digitally, you need at
least two sample points for each cycle of the waveform--one for its peak, one
for its trough--in order to reconstruct it in anything approaching a
recognizable form.

Thus, in order to distinguish those 320 lines (you can treat them as either
320 white lines against a dark background, or 320 dark lines against a white
background), you need at least 640 pixels.

Lawrence D'Oliveiro                       fone: [phone]
Computer Services Dept                     fax: [phone]
University of Waikato            electric mail: [e-mail]
Hamilton, New Zealand    37^ 47' 26" S, 175^ 19' 7" E, GMT+13:00
And in my heart I'm thinking, lub-dub, lub-dub, lub-dub...