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From: stever@videovax.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: NTSC standard
Message-ID: <4237@videovax.Tek.COM>
Date: Wed, 18-Feb-87 19:14:48 EST
Article-I.D.: videovax.4237
Posted: Wed Feb 18 19:14:48 1987
Date-Received: Fri, 20-Feb-87 06:47:44 EST
References: <1235@husc6.UUCP>
Reply-To: stever@videovax.Tek.COM (Steven E. Rice, P.E.)
Organization: Tektronix Television Systems, Beaverton, Oregon
Lines: 40

In article <1235@husc6.UUCP>, Justin J. M. Grunau (grunau_b@husc4.UUCP)
writes:

> Forgive my ignorance, but all this recent discussion about the Amiga's NTSC
> standard has got me confused.  . . .

> But this confuses me -- I understand that NTSC standards will not allow a
> 640 by 400 non-interlaced display;  but I thought the Amiga was famous for
> having not only NTSC output, but also digital and analog RGB, which are,
> unless I am confused, NOT NTSC-compatible.  Could somebody enlighten me on
> the distinction? 

NTSC is an acronym commonly used to refer to the National Television
System Committee's report #7, and the color transmission standard it
specifies.  By reference, it includes the previous monochrome (black-and-
white) system standard, though with slight modifications.  Thus, an NTSC
signal is 29.97 frames/second (usually called 30 frames/sec) with 2:1
interlace (which means 59.94 fields/second).  The color subcarrier is
3.579545 MHz.

The RGB output of the Amiga, while not directly NTSC-compatible, has the
same timing as the NTSC output.  (If this were not the case, it would be
necessary to have two sets of video output generation circuitry, and at
least twice as many display ram accesses for each pixel.)  The RGB output
signal can be directly converted to NTSC (though with some loss of
resolution, because the bandwidth of an NTSC signal is not adequate for
medium- to high-resolution images).

A point that should be made: as the resolution and the line rate of the
display are increased, there is a dramatic increase in both the amount of
display RAM required to contain an image, and the bandwidth of the channel
from memory to the display.  If the display is interlaced, the output data
rate is half that required for a progressively-scanned display.  Doubling
the display data rate of the present Amiga would be an expensive
undertaking, probably moving the Amiga out of the consumer price range.

					Steve Rice

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