Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!sgi!chandlee@alpine.SGI.COM
From: chandlee@alpine.SGI.COM (Chandlee Harrell)
Newsgroups: comp.sys.sgi
Subject: Re: videotaping from the iris
Summary: perhaps some further clarifications (or deepening the murk)..
Message-ID: <22213@sgi.SGI.COM>
Date: 18 Nov 88 04:48:40 GMT
References: <8811020355.aa14353@SPARK.BRL.MIL> <16683@onfcanim.UUCP>
Sender: daemon@sgi.SGI.COM
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 44



  Iris 3000s are shipped with two video options.   The two defaults
  provide video timings for 1280 by 1024 60hz monitors and 640 by 480
  RS170/NTSC monitors.    A customer can request that the RS170
  option be replaced with either PAL/SECAM timings or for a 1280 by
  1024 interlaced 30hz monitor.

  All Iris 4D systems ship with all four of the above timing options.

  When in RS170 mode, the Iris outputs the three components of RGB
  in the correct RS170 timings, un-encoded.   The bottom leftmost rectangle
  of 640 by 480 pixels is displayed on the full RS170 monitor screen.

  An option board may be purchased from Silicon Graphics for Iris 4D 
  systems which takes the three RGB outputs and color encodes them
  into a composite video signal.   This signal is appropriate for
  connecting directly to any television, or to a VCR.   The composite
  video output does not match up to broadcast quality; there is some
  minor difference that I am not familiar with.   This should only be
  a concern for the media organizations, not for those of us creating video
  presentations.   (Otherwise one buys a much more expensive broadcast
  quality color encoder.)

  This option board is called (internally, at least) the CG2/3.  It
  also provides the genlocking capability.   This is the capability to
  sync up and overlay the video from two separate systems (while in
  either high res 60hz or NTSC modes).

  So option one for video taping on an Iris 4D is to buy a CG2/3.  
  The bottom left quarter of the screen may be recorded directly into
  any recording device that accepts NTSC composite video.

  Option two allows you to video tape the full picture on your 1280 by 
  1024 high resolution display.   Pixel averaging is done to reduce
  4 pixels down to one giving the appropriate number of pixels (640 - 480)
  for NTSC.   Pixel averaging provides better images over simply drawing
  the image into the bottom leftmost portion of your screen because a
  certain amount of anti-aliasing takes place in the pixel averaging.
  It also allows full screen video taping.   Option two is available
  from vendors like RGB Technologies (don't know their pricing).  The output
  from these systems is, again, standard composite video.    Note:
  Silicon Graphics has some ongoing development that should help
  those desiring the pixel averaged approach.