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Path: utzoo!utgpu!water!watmath!clyde!rutgers!ames!sdcsvax!hutch
From: hutch@sdcsvax.UUCP
Newsgroups: comp.graphics
Subject: Re: NTSC converters
Message-ID: <3263@sdcsvax.UCSD.EDU>
Date: Wed, 3-Jun-87 01:21:31 EDT
Article-I.D.: sdcsvax.3263
Posted: Wed Jun  3 01:21:31 1987
Date-Received: Fri, 5-Jun-87 03:04:14 EDT
References: <1208@batcomputer.tn.cornell.edu> <2049@utah-gr.UUCP>
Reply-To: hutch@sdcsvax.UCSD.EDU (Jim Hutchison)
Distribution: na
Organization: UCSD EMU Project (Educational Microcomputer Unix)
Lines: 39
Keywords: NTSC, RGB, Video

Thus sayeth Spencer Thomas in article <2049@utah-gr.UUCP> (thomas@spline):
>So spake (James Ferwerda) verily <1208@batcomputer.tn.cornell.edu> (jaf@squid.tn.cornell.edu):

>>a way of converting our 1280 X 1024 X 24 bit RGB images into some NTSC
>>compatible format.

>Cain't be done.  NTSC only applies to "525" line systems.  You need a
>frame buffer that has approximately 480 lines in the vertical
>direction, and a 30Hz interlaced scan (i.e. 60Hz field rate).

Well, yes & no.  Lyon Lamb supposedly sells a nice little widget that
will convert gold (high res RGB) into lead (NTSC).  Basicly it is a
frame buffer and some signal conversion gear.  The 1280 is just pixel
rate conversion, the 1024 is black magic to me (deep analog magic, or
dropping lines?).

Presuming that you know you will be losing colors and pixels in the
conversion, I can't see why it is impossible.  I am not berating
Spencer, perhaps I have missed his meaning.  Important note, you get
about 424 color changes in the horizontal direction.  There is also a
limitation on how close together you can put color changes.

It is all nasty analog biz, look at the equations/definitions and
calculate how far you can push it before the chroma starts sneaking
into the luminance.  The number of changes is a function of how much
the signal knows and *guesses* about the contents of a scanline.  Yup,
NTSC guesses.  More nasty biz, when it is sliding through a sync pulse
it is also continuing with the last thing it knew to display (color &
luminance-wise).

Well, along with Spencer's suggested reading, you might also look at
the NTSC spec from EIA, the SMPTE journals are another suggested source.
I'm no master, just saying a piece in the name of the revolution.
-
-- 
    Jim Hutchison   		UUCP:	{dcdwest,ucbvax}!sdcsvax!hutch
		    		ARPA:	Hutch@sdcsvax.ucsd.edu
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