Single-frame video recording from an Iris

[Mike Muuss]

In a recent note, Stuart Levy writes:

>> From what I hear, super-VHS is supplanting 3/4" tape.  (In fact, JVC and
>> Panasonic are discontinuing their 3/4" lines.)  SVHS uses Y/C component video,
>> with two channels on the (1/2") tape, one each for luminance (Y) and chroma (C)
>> plus the usual audio stuff.  SVHS is supposedly higher resolution than 3/4"
>> but somewhat worse noise.  The difference is apparently not large, but
>> SVHS equipment is decidedly cheaper.  ...

This is somewhat misleading.  3/4" U-matic tape is also recorded
as separate luminance (Y) and chroma (C), as is regular VHS, Super-VHS,
and many other formats.  The differences between these formats are
in terms of bandwidth available for each signal, and signal/noise ratio.

While some very low-budget operations have begun mastering on S-VHS,
there is no question that S-VHS is a lower quality format than 3/4".
A 5th or 6th generation dub on 3/4" is still of acceptable quality
(although not prizewinning), while the same can not be said of even
a 3rd generation S-VHS dub.  Certainly not with any S-VHS equipment that
I have worked with.

It is important to note that the Y/C bandwidths on 3/4" come in two
flavors as well.  Regular 3/4" has about 260 lines of resolution
(e.g. about 520 pixels/scanline), while SP-format 3/4" has about
360 lines, or about 720 pixels/scanline.  The NTSC format is
bandwidth limited by law to have no more than 720 pixels/scanline,
so this is as good as it gets in real NTSC.  Wider bandwidth signals
can be easily created in your studio (the "multiburst" signal from
most test sets is an example), but it isn't real NTSC.
Thus, the SP version of 3/4" fills roughly the same need for 3/4"
users that S-VHS serves for VHS users, but with the 50 dB video S/N
and tape speed stability of the 3/4" format.

A QUALITY COMPARISON:  Subjective, and Measured.

Just last week, I had the opportunity to make several dubs of my recent
video, and used this chance to compare S-VHS to regular (not SP) 3/4".
I tried to give the S-VHS dub every advantage. I used my NEC 1000 S-VHS
machine ($1000), which I have measured as having about 375 lines of
resolution in S-VHS mode (i.e., full NTSC bandwidth) on the composite
NTSC input. Note that the manufacturer claims this machine to have "425
lines of resolution" when fed a non-band-limited S-Video (Y/C) input
signal (which is hard to come by).

I connected the output of the 1" mastering machine directly to the
composite NTSC input of my S-VHS deck, and used TDK's best S-VHS tape.
Hi-Fi sound was also taken straight from the 1" machine. (BTW, 1"
machines have rather mediocre sound, ~45 dB S/N, compared to better than
80 dB S/N on a Hi-Fi VHS or S-VHS deck). Next, I also made a copy on
3/4", through the regular distribution amps, i.e. I had additional gunky
circuitry in the signal path over the S-VHS dub.

Comparing my S-VHS dub to the 3/4" dub requires no special talent.  The
S-VHS copy is *much* noisier than the 3/4" copy.  And recall, this
is conventional 3/4", *not* the wider bandwidth SP format. The S-VHS is
still quite good to look at, but not nearly as nice as the 3/4". If you
are accustomed to viewing NTSC only on VHS tape, you would not be upset,
but if you are accustomed to viewing NTSC as it exists in the mastering
process, you would mourn the loss.

However, it is true that 3/4" is no longer the best way to capture video.
In order of increasing quality, the competition comes from Hi-8,
Betacam SP, D-2 digital, and D-1 digital.  Betacam SP is a "component"
video system, recording Y, R-Y, and B-Y signals, rather than Y and C.
D-2 is a "composite" (Y/C) digital format, and D-1 is the "component"
(Y, R-Y, B-Y) digital format.  D-2 decks are now available for less than
$50k, and the prices are comming down.  Since a good 3/4" machine costs
from $10k to $30k, this isn't such a large price difference (reference:
the Sony BVU-850 and BVU-870).  Note, however, that while the digital
formats offer zero generation loss, the digital format has inherrent
quantization, which can be quite noticable in the D-2 format.
8 bit samples are just not wide enough;  we need 10 or 12 bits
to satisfy the discerning eye, even with dither used to prepare
the original signal.

Mind you, I'm no big fan of NTSC -- it is a very limiting, low quality
video format.  But, it has supplanted 16mm film (a superior quality
format) as the standard way of communicating scientific results,
so one might as well understand it, and master it.  NTSC, when done
well, can be a very striking and effective way of communicating.

AN EXAMPLE OF MAKING A VIDEO

Just to give you a quick idea of how I created my recent video:

Images were created in RGB at 1280x960, and decimated using a 5x5 filter
kernel down to 640x480.  These RGB images were converted to Y/U/V format,
the U and V data was low-pass filtered to meet NTSC bandwidth limitations,
and the YUV data was transmitted over Ethernet to an Abekas A60 digital
video disk ($60k), where they were stored in D-1 digital video format.

When an entire segment of video had been loaded onto the Abekas, it
was played back in real time, under control of an FCC-approved broadcast
quality sync generator.  The RGB outputs of the Abekas were sent to a
Faroudja CTE-1 RGB->NTSC encoder ($7k), and the composite NTSC was
recorded on a Sony BVU-870 3/4" VTR ($30k) with SMPTE time code generator.

Real-time sequences were captured from an SGI-4D/240 GTX ($100k) with
CG3 board ($7k?). The sync pulses were fed into the CG3.  With the SGI
in NTSC mode, genlocked to "house sync", it provided RS-170 RGB, which
was fed into the Faroudja encoder, and the composite NTSC was recorded
on the BVU-870. I note in passing that the CG3 still does not succeed in
producing broadcast quality video, although it is far better than
earlier attempts.  Unlike earlier SGI CG boards, the output of the CG3
is sufficiently good that it can actually be used, if you don't mind
"tweeking" the Faroudja into forgiving SGI's sins.

Each segment went onto a separate 3/4" cartridge, and all were indexed
event-by-event according to the time codes.  This allowed the script to
call for segments to be assembled with individual frame accuracy.
(Allow me to make a BIG PLUG for the use of SMPTE time code on your
video tapes.  It makes the editing process vastly easier, and more
accurate).

All the 3/4" original tapes went into a big box, and I took it all to
our 1" edit suite.  The original tapes were read on a pair of Sony 3/4"
machines (VO series), stablized by a time base corrector (TBC), routed
through an edit controller with Ampex effects box (for fades and wipes)
and Ampex ADO (for inset screens, flip-away effects, and "MTV" style
rotating and tumbling images), after which each finished sequence was
recorded on an Ampex 1" machine ($50k).

After the video was complete, I added the music to Channel 1, going from
Compact Disc to the 1" machine via a sound board, where the mix to mono
was accomplished. Then, I recorded the narration in a sound booth, onto
a 3/4" tape. Using the same edit system, the narration track was copied
onto the 1" machine (although I'm proud to say that in 8.5 minutes of
narration, I only made one "flub" that we had to splice in a replacement
for.  This was done using the edit system, just like editing video).  At
this point, the master tape was finished.

Dubs for the final distribution were made from the 1" master onto 3/4"
and VHS, through a 1->12 video and audio distribution amplifiers. Thus,
the distribution copies delivered to the clients are only 3rd
generation. Since the trip from 3/4" to 1" is "nearly lossless", the
distribution copies have excellent quality. Given that, in my instance,
distribution is done on 3/4" and VHS, increasing the quality of the
intermediate steps is not likely to make a noticable improvement in the
quality of the product.  The 1" master would be completely suitable for
broadcast.

Even if you don't have the financial resources to engage the services of
a 1" edit suite for your video productions (not that it is very
expensive), and you do all your production and editing in 3/4", you will
get a high quality result.  Certainly better than anything you could produce
on Super-VHS.

FRAME AT A TIME

In the past, I have also done quite a bit of frame-at-a-time recording
of video, using the Sony 3/4" machines and a Lyon-Lamb VAS-4 VTR controller.
This produces results of equal quality (all other elements being equal),
but takes longer.  It is also more of a bother to find and fix botched
frames when recording this way.  It also requires a much smaller
investment in equipment!  ($5k for Lyon-Lamb Mini-VAS, plus a VTR).

LASER DISCS

On a related topic that I won't bore you with this evening, I recently
investigated the quality of LaserDisc players.  They are much better
than consumer videotape (even Beta), but 3/4" tape does even better.
The machines evaluated were the Pioneer CLD-91 ($2000) and Pioneer
CLS-S2 ($3500) [the worlds finest Laser Disc player at the moment].

SUMMARY

*)  3/4" videotape is no longer the best thing around.
*)  3/4" can be used to produce excellent results.
*)  3/4" beats S-VHS every time (video, not audio).
*)  3/4" is mature, and not too expensive.

Many alternatives exist, and lots of good stuff is happening.  Keep your
eyes on Betacam SP and D-2.  If you have (or are) a good video engineer,
there are lots of alternatives.  If you don't have access to a good
video engineer, the business of video recording still has a lot of
pitfalls, and it will pay to be very conservative.  Be suspicious.

Also, most large universities and companies have a TV studio, and there
are many commercial firms in the business.  Strongly consider using them
to assist with your post-production needs.  The aid of a professional
video editor (person) can greatly increase the quality of your result;
knowing when and how to use fades, wipes, etc, is more of an art than a
science. Rates are generally in the $100/hour to $200/hour range, and
often less.

	Best,
	 -Mike Muuss

PS:  In case you are interested, all the image generation software,
image filtering software, Lyon-Lamb controller software, etc are all
included as a small, but significant, part of the BRL-CAD Package,
which we make available for free.  See SGI's software partners catalog
for details, or send E-mail.