videotaping from the iris

[Phil Dykstra]

What we are presently using here for NTSC from an Iris is a Lyon-Lamb
ENC-VI NTSC Encoder (cost ~4500).  In my opinion, there are higher
quality encoders on the market (RGB Technologies, Faroudja CTE-N), but
this is one of the cheapest (and includes a Sync generator and Black/
ColorBars generator).  In software, you need to set the Iris for 30Hz
interlaced (which means that the main monitor becomes useless until
you go back to 60Hz).  You get the lower left hand corner of the screen
(~640x480 pixels).

If you want the full IRIS screen to come out in NTSC you will need a
"frame scan converter".  These are more expensive (~25k).  See e.g.
Photron.

SGI also sells an RGB -> NTSC encoder board for the 4Ds.  We bought
one but sadly have not been able to use it.  Why is because the SGI
board outputs a fully positive video signal (i.e. blanking is around
+0.3V) rather than a bipolar signal with blanking at 0VDC.  While
I haven't found anything in the RS170A spec that requires an absolute
voltage level (it all looks to be AC coupled), much to my surprise our
Sony BVU850 seems to REQUIRE blanking to be at 0VDC (or at the very
least average picture level to be at 0VDC).  Black levels get all
messed up when recorded from the SGI board but come out okay from the
ENC-VI.  I don't know who's to "blame", if anyone, but its something
to keep in mind.  [nothing works the way it is supposed to]

- Phil
<phil at brl.mil>
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