From: pustule@cats.ucsc.edu (Thaddeus H. Wood)
Newsgroups: comp.graphics.animation
Subject: Computer Graphics and Video: Creating New Effects
Date: 13 Oct 1992 21:49:34 GMT
Organization: University of California; Santa Cruz
Distribution: world
NNTP-Posting-Host: as215-ws-2.ucsc.edu


Sep 21 169 lns
Computer Graphics and Video: Creating New Effects
By Greg Estes
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  The convergence of video and computer graphics is well known within each
respective industry. Ask any video industry leader what issues are facing
manufacturers, vendors and end-users of video equipment, and the connection
between computers and video gear is bound to arise.
  Everyone knows that computers are affecting the video business -- they're
just not quite sure how. Will fast computer disks replace VTRs? What effect
will "Multimedia Personal Computers" have on the industry? Is there a whole
new audience for video-based information services?
  The list of questions is long, but far-sighted video equipment
manufacturers are looking to either leverage computer technology or, if not
partner with computer companies, at least peacefully co-exist. This is
because software and hardware that will turn computer workstations into high-
quality special effects and video image processing stations -- areas
traditionally dominated by dedicated video hardware -- are becoming
available.
  The trade-off in the past has been that stand-alone video hardware was
capable of a limited number of processing functions but provided high quality
and the kind of user interface that felt comfortable to video production
people. Computers offered easy board-swap upgrades, lower cost and a wide
array of special effects possibilities, but users were often burdened with
unfamiliar interfaces and less-than-broadcast quality.

REVERSE MULTIMEDIA?
  On the computer industry side, the interaction with audio and video has
become something of a Holy Grail. Hardly a week goes by without some computer
manufacturer shouting, "THE PROMISE OF MULTIMEDIA HAS ARRIVED!" This, of
course, means nothing to a computer user and even less to a video person.
  Despite this, the computer industry is ripe with products that will bring
video to personal computers and workstations. These products can often be
great tools for communication, training and integrating video images into
documents of various kinds.
  However, computers today are affecting video more for real applications
than the integration of video and audio is affecting computers. So the big
deal may not be video on the computer, but rather computer graphics on video.

COMPUTER ANIMATION
  Powerful computer workstations capable of 3-D graphics have been used for a
number of years to do single-frame animation. Characters or logos were
modeled in 3-D and manipulated as wireframes in real time for motion tests,
but for final production work each frame was rendered separately.
  Frames of animation were rendered directly to videotape or, more often, to
a digital disk recorder or perhaps a laserdisc. The resulting image files
could be processed as video rather than computer information on dedicated
hardware designed to manipulate traditional video sources.
  While this is still the way the lion's share of computer animation is
produced today, it's just the beginning of the story. Today, modeling,
rendering, animation, compositing and effects all can be done on a single
computer workstation.
  Animation and special effects companies like Pacific Data Images, Rhythm &
Hues and Industrial Light & Magic use the digital compositing and video I/O
capabilities of computer workstations to accelerate both the creative and
production processes. Graphics supercomputers like Silicon Graphics'
PowerVision series are capable of compositing incoming analog and digital
video with real-time 3-D graphics, so CGI can be combined with live action
and processed together in the computer. This enables users to audition
effects, create interactivity between live actors and computer puppets,
colorize or color-correct movies, and handle many other processing jobs such
as wire removal or perspective correction -- all on their computer screen.

THE IMPORT/EXPORT BUSINESS
  For video work, images can be transferred from D1 videotape masters to an
Abekas A60 digital disk recorder. This enables the transfer of frames or
fields of digital video from the disk to the host computer over Ethernet. The
images are then sent through a colorspace conversion from the 4:2:2 digital
YUV, which the D1 VTR or disk recorder can generate, to the RGB, which the
computer can display.
  Although this method is widely used, it has some drawbacks. The disk
recorders usually record only 25 seconds of video, and it takes a number of
seconds to import or export each frame. However, Abekas has recently
introduced the A66 disk recorder, which offers twice the storage capability
for less money. But the A66 does not offer an Ethernet port.
  Recently, however, Silicon Graphics announced VideoLab, a video I/O board
for the Iris PowerSeries computers that can digitize the incoming 4:2:2 at 30
fps. This capability eliminates the need for the Ethernet port, since the
digital YUV can be imported in real time directly from either the D1 master
or the disk recorder.
  Once the frames are loaded in the host computer, the number of composites
becomes almost limitless. Multiple channels can be imported into the system,
and live action can be made to "interact" with 3-D character animation.
  From simply combining images from different sources to rotoscoping,
character generation and everything in between, bringing video into the
computer offers incredible flexibility. The images still must be sent out as
video (or film), however, and that is where the plot thickens.
  Most computers do not have disk drive subsystems capable of bringing up
full-sized images from the hard disk and out to the display system in real
time. Once the information is in the computer's frame buffer, it can be
viewed as RGB on the computer monitor or sent out as video. This means that
unless incoming video can be processed at 30 fps and "passed through" the
computer system, the output must be as a series of frames over Ethernet
(again to an A60 or similar device) or through the frame buffer in
conjunction with an animation control system.
  Tape control systems for computer animation often use either the RS-232 or
RS-422 ports to control VTRs directly from the computer. This is a time-
consuming process, but the frames can be rendered in the background so that
the computer does not need to be dedicated just to dumping frames to tape.

REAL-TIME AND SINGLE-FRAME EFFECTS
  Perhaps the hottest special effect now in the public eye is the "morph"
effect. Morph effects, or metamorphosing one image/character into another,
have been used in a number of works lately. Perhaps the most notable have
been ILM's "Terminator 2" special effects and, most recently, the stunning
transformations of actors of various nationalities for the Michael Jackson
"Black or White" music video from PDI.
  Although the success of these spots is sure to have the phone ringing from
agencies requesting similar effects, Ray Giarratana, senior animator and
technical director at Pacific Data Images, noted that there is no magic morph
button that can be pushed for any particular situation.
  "There's really no one thing that you would call morph," he said. "It's
really a lot of different techniques that are used that together become the
effect that you see on video." He also pointed out, "Every [effect] is
different and has different problems and circumstances."
  These circumstances can create special challenges for animators. For
instance, the 3-D graphics generated from the computer can be too "clean"
compared with film. Film and video can have various inaccuracies that can be
difficult to replicate in the precise world of computer-generated images.
  To this end, PDI has created special software that can add grain to make
the computer-generated images match the film. The concept involves adding
realism by adding imperfection. This is akin to the way musicians combine
short samples of real instruments with synthesized textures to create sounds
that are more effective than if they were purely real or purely synthesized.
  Compositing live-action images and computer graphics can involve more than
just keying or blending the images together. Matching the look and feel of
the video can involve sharpening or blurring the background, applying an
environment map so that the live-action sequence is reflected in the 3-D
animation, or any one of a number of image processing functions. Environment
mapping, or reflection mapping, is a process that can greatly add to the
realism of computer imagery.
  A common process in creating realistic CGI is to apply textures to a given
piece of computer geometry. These textures are typically real-world images
imported from a frame grabber or a scanner, although they can be completely
computer generated if so desired.
  For instance, a computer-generated sphere could have a leather texture
applied to it to create the impression of a baseball. With a texture map,
when the geometry moves, the associated image moves with it in complete
perspective.
  With environment mapping, geometry can be assigned surface properties that
can in turn be made to reflect other images. A shiny car can be made to
reflect the lights from a showroom floor. If the car moves, the lights stay
in one place but they are reflected in different ways based upon the new
position of the moving car. This process is very effective in creating a
sense of continuity and realism in a scene.
  Rhythm & Hues used texture mapping in conjunction with sophisticated 3-D
modeling and lighting to create the Lexus advertisement in which the outer
skin of the existing Lexus ripples away in the wind like a blanket, revealing
the new Lexus.
  The result of these incredible special effects is an upping of the ante,
with increased expectations from the viewing public. Viewers were dazzled by
the computer-based effects in such films as "The Abyss" and "Terminator 2,"
but show those same effects to them again and there may be a collective yawn.
  That is where the true artistry of the effects wizards comes in. The
difference between great effects and good effects is in the creative process,
in addition to the hardware capabilities of a particular system. Rhythm &
Hues' rippling Lexus spot was not spectacular just because of the advanced
CGI/live-imagery blending software, the lighting source models or the digital
pixel manipulation, but also because of the innovative ideas behind them.
  The digital video capabilities of new computer systems are both production
tools and, perhaps more importantly, aids to the creative process.
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  Greg Estes works with Silicon Graphics' Advanced Graphics Division.
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  Reprinted with permission from the Spring 1992 issue of Iris Universe
magazine.
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Copyright 1992 by HPCwire. All rights reserved.

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Just an interesting article I picked up.

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Thad