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October 1997, Week 2


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Dave Trautman <[log in to unmask]>
Reply To:
Film and TV Studies Discussion List <[log in to unmask]>
Wed, 8 Oct 1997 09:59:51 -0600
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Jeremy Butler wrote,
>What I should have said is that *digitally* captured images from
>*video-originating* material are superior to analog
>photographs-of-the-monitor images of the same.  What Chuck Derry and I have
>been trying to figure out is a good way to get video images (not film
>images) into print.
Ah, finally something I know something about.
I was going to come into the thread and castigate Jerry for misleading
the group about video images but he has redeemed himself through his
clarification.  However, I think the list would benefit from a little
tech talk about this in case you're preparing to take the plunge into the
muddy waters of video capture for printing.
Let's start with video itself.  I often describe video in my seminars as
looking at life through a screen door.  It's fuzzy.  Really clean,
original video is fuzzy.  Even NHK's 1125 HDTV is fuzzy (in a manner of
speaking) closer than 3 feet.  If you were to have a TV screen in a book
in your lap you'd be able to see the lines and the fuzzy edges.  We
normally watch TV screens from about 6 feet away and the specs for NTSC,
with respect to clarity, are interpreted for a minimum of 6 feet viewing
The second barrier to scramble over is the player machinery.  A paused
video image is not the whole signal.  An image running at play speed has
about twice the signal information as a paused image.  A captured frame
ought to be running at full speed when it arrives in the computer then it
can be selected from the "stream" as a single interval.
The third barrier to haul yourself through is the quality of the capture
encoding hardware.  The highest quality capture systems cost plenty.
They capture excellent images and convert to digital without adding any
artifacts to the signal.  Capture systems for non-linear computer editing
are top notch and top priced.  They capture each frame individually,
which is necessary for editing as you can well imagine.  Some capture
"streams", are not frame-based, and need to have more than a single
frame's information to reproduce a still.  But that's another essay.
The next obstacle on the course is the compression of the captured file.
If you have the real estate on your hard drive (or server system) you can
capture the image stream without any compression and save it to a disk
directly.  We're talking big big big files here.  I have a one gigabyte
file which represents a 720 pixel by 480 pixel image size capture of a
Betacam original tape segment lasting only about 5 minutes.  It's
beautiful and clear, but it's trapped on my AV speed drive because I can
barely squeeze it onto a JAZ removable cartridge.
Most software which operates capture systems offers you a pallette of
compression schemes.  If you compress the file when saving, you're going
to lose image.  Fuzzy originals become worse when compressed.  Getting
that one frame from the stream (the uncompressed one you make) means
having software which will "clip" that frame and make an image file from
it.  Some software hasn't a clue what you need.  Other stuff is helpful
or will handle plug in software to help with the transitions.  However,
most plug in technology is developed to get graphic files into video and
not video files into graphic formats.
Long before you play the tape into the computer you should have had the
kind of meaningful conversation with your graphics professional you would
normally have with your spouse concerning family planning.  This intimate
exchange should include their preferred file type, their need for
"screen" parameters, and a discussion of the final use of the image in
the printed document.  They may ask that you capture as big and deep a
picture as you can afford so that they later can reduce it, enhance it,
and then compress it.
It's only one frame afterall.  How big can it be?
The final hurdle before the finish line is the graphic output.  My
graphics professional has found a process in which he "shrinks the image"
by some magic percentage and increases the "perceived" clarity of the
image, then he weaves his enhancement magic on the file and compensates
for much of the contrast, colour edges, and in-frame motion artifacts
using all those "curves" and spikey image charts.  He shrinks the picture
in order to create a more dense set of pixels.  This improves the
apparent sharpness of the image.
He handles all the friction between himself and printer without my help.
They speak that foreign tongue of screens, dots, ink bleed, and paper
quality which I never learned in school.
If anyone wants details on the hardware a person normally needs for this
(or maybe just the stuff I use) they can mail me for it.  Have a cheque
book handy because these things don't come cheap.  If you have an
inexpensive, consumer level capture system you won't be happy with the
results of video captures becoming graphic files.  You can take that to
the bank.
I haven't found a store-front service in my area which either understands
enough of the process or has the hardware or software to do an adequate
job.  These are rare skills.
Dave Trautman
Media Specialist for ATL
University of Alberta
Edmonton, Alberta, Canada
Screen-L is sponsored by the Telecommunication & Film Dept., the
University of Alabama.