Newsgroups: sci.image.processing
From: paul@pcserv.demon.co.uk (Paul Carpenter)
Path: cantaloupe.srv.cs.cmu.edu!europa.chnt.gtegsc.com!news.mathworks.com!news.alpha.net!uwm.edu!math.ohio-state.edu!howland.reston.ans.net!pipex!peernews.demon.co.uk!pcserv.demon.co.uk!paul
Cc: sggoodri@unity.ncsu.edu
Subject: Re: S-Video versus RGB quality
References: <3lt3i8$am9@taco.cc.ncsu.edu>
Organization: PC Services
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Date: Wed, 5 Apr 1995 10:04:09 +0000
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sggoodri@unity.ncsu.edu "Steven Georg Goodridge" writes:
-I am trying to be a cheapskate, using basic multimedia capture cards for
-color computer vision under OS/2.

Yes!

 So far, I have found that S-video
-gives me good captured images, with little noise in the color from
-frame to frame. NTSC was not very good, with successive frames giving
-slightly different colors, which caused problems.

Hence one of the acronyms for NTSC being "Never twice same colour", and also
why PAL uses different coding technique to remove such problems. (Not 
recommended method for 24 bit colour). Depends on your resolution for your
application.

 My application
-involves color difference for motion detection, and color histogram
-matching for object classification. I am using 24 bit/pixel RGB
-images (bitmaps).

I wonder what the histogram has in the way of holes/spread/bin weigthing when
viewing colour gradients (RGB black to Red, black to Blue.. separately)

-I know that RGB is the most common signal used by color image procesing
-systems, but this hardware is more expensive than S-video. Most of the
-documentation I have found on video signal qualtiy refers to the what is
-perceived by the human eye, not the machine. So I wonder is anyone can 
-answer a few (simple?) questions:

Because these systems are designed on viewability not measurability, where 
reductions could be made to save on bandwidth and complexity, but still be 
viewable and allow the eye/brain integration to compensate for the reductions.

-1) What is the quality advantage of RGB over S-Video, that I am likely to
-notice in computer vision applications?

Better bandwidth and resolution from true RGB source.

-2) Are these advantages related to the camera (ie multi-chip) the signal
-format (bandwith limitations) or the encoder/decoder circuitry?

All of them, as multichip gives better response (no loss of light due to 
striping), bandwidth as colour difference signals (colour encoding) uses reduced
bandwidth as eye cannot detect colour changes to the same detail as luminance 
changes.

-3) Does anyone have comments on using S-Video for color image capture
-and processing, good or bad?

S-Video from camera or tape?

S-Video is better than NTSC/PAL for bandwidth but not as good as RGB for
measuring purposes, but that depends on what you need to measure down to.

S-Video from SVHS and like VCRs has colour bandwidth reduced to below 1MHz on
most domestic type VCRs less than 500KHz, the luminance is often reduced to at
best 3MHz. Instead of luminance 4MHz+ and colour 2MHz+.

Above all else it depends on your applications quality criteria as to whether 
the S-Video format delivers the required resolution to suit your needs. Only you
can judge this, by comparisons, and knowing what you require.

----------------------------------
Paul Carpenter
PC Services, UK
 - "Any people you should meet are the products of a deranged imagination"
