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From: karn@petrus.UUCP
Newsgroups: net.video,net.analog
Subject: Re: Q-channel bandwidth
Message-ID: <304@petrus.UUCP>
Date: Tue, 5-Mar-85 14:35:26 EST
Article-I.D.: petrus.304
Posted: Tue Mar  5 14:35:26 1985
Date-Received: Wed, 6-Mar-85 04:58:45 EST
References: <146@unccvax.UUCP>
Organization: Bell Communications Research, Inc
Lines: 14
Xref: watmath net.video:1036 net.analog:184

My understanding of the reason for the different I and Q channel bandwidths
is that it was based on human visual perception. The human eye is much
more sensitive to changes in intensity and hue for some colors (e.g.,
flesh tones) than it is in others.  The I and Q axes were arranged so that
the I channel carries the information requiring wide bandwidth (reddish-yellow
flesh tones and their complements) while the Q channel carries blue-green
signals and their complements.  The eye is much less sensitive to bandwidth
restrictions in the Q channel.

Given its age, NTSC is still a remarkable tradeoff between human factors
and engineering constraints, which is even more amazing when you consider
that it was produced by committee.

Phil