suits and magic bubbles: Behind the scenes of Sabrina Down Under
David Hickey and Trent Shumway
September 26, ABC aired Sabrina Down Under, the third telefilm
staring Melissa Joan Hart as America's favorite teenage witch.
Directed by Ken Koch on location in Australia, the film
was the most technically ambitious in the series so far, featuring
logistical hurdles such as underwater and aerial photography.
The visual effects crews at Modern Videofilm and LightPoint
Entertainment were asked to deliver shots ranging from a magically
conjured typhoon to motion-captured 3D character animation.
of the most difficult sequences in the movie was when Sabrina
and her best friend Gwen (Tara Charendoff) were scuba diving
on the Great Barrier Reef. Sabrina tries to talk to Gwen but
can't because they are underwater. To solve the problem, Sabrina
blows air bubbles out of her mouth, then uses magic to enlarge
one of them until it is big enough for the girls to swim inside.
With their heads poking inside the bubble, the girls can talk
while watching the fish swim along the reef.
The shots were completed using several components. The production
crew provided plates shot with the actresses swimming on the
reef, along with matching bluescreen footage shot by Australian
effects supervisor Lynne Cartwright. The second unit
crew provided footage of fish swimming on the reef, and air
bubbles shot against black. Modern Videofilm's staff artist
David Hickey created the "magic" bubble using 3D animation.
bubble effect was accomplished in Alias|Wavefront's Maya, using
a combination of keyframe animation, dynamics, soft bodies and
hard bodies as collision objects," said Hickey. The overall
sequence of creating the bubble effect was to first create a
primitive sphere with increased subdivisions for greater detail.
The sphere was animated in reference to the backplates, then
converted into a soft body. All primary physical animation is
performed on the hard body objects. Secondary dynamic animation
is performed on the soft body.
The animation of the hard body was accomplished by animating
both their transform node and also in some sequences, animating
the control vertices of the sphere. Once the animation was matched
in reference to the backplates, the hard body was converted
to a soft body. A turbulence field was added to the soft body
to add some arbitrary secondary movement. Interaction between
the live actors and the 3D bubble was created using modified
invisible primitive spheres as collision objects.
In pre-production , Executive producer Paula Hart explained
that she wanted the magic bubble to look different then other
air bubbles in the water. She wanted it to look like a soap
bubble floating in the air. To create this look, the bubble
was textured using various maps and original backplates. The
main shader was a dark blue color at ninety-five percent transparency.
An animated water map was used as a bump map to add additional
ripples throughout the bubble. A rainbow hued noise ramp was
applied to the secularity to enhance the prism effects of the
highlights. And finally, the scene backplates were used as an
animated reflection map.
For the shots where the actresses were within the bubble, Hickey
had to render the effect for each shot in six different pieces,
because the actresses needed to be sandwiched between the layers
of the bubble. This gave the illusion of distortion and reflection
in front and behind them, and gave Henry artist Trent Shumway
the extra control he needed in compositing. Additive keying
seemed to retain the transparent nature of the bubble while
allowing the different soap like colors and keeping the highlights
brilliant and opaque.
"The thing that we were bumping into was the amount of black
that was used in the wardrobe," Shumway said. "The solution
seemed to be to render it over blue; combining the luminance
and additive keys." This process retained all of the girl's
reflections. Mattes were also needed for the front and back
pieces. These mattes allowed Shumway to distort and apply a
slight color correction to the back -plates. The idea was that
whatever was inside the bubble would be slightly warped and
less murky then the surrounding environment. Obviously, whatever
was supposed to pass behind the bubble had to have these same
adjustments. It became easier to comp those elements first then
apply the setups overall.
couple of fish and bubble elements were selected and then composited.
Shumway then simply plotted a point right in the middle and
pushed it back in Z space. When elements traveled from beside
the bubble to behind it there was a slight offset, giving the
movement a three-dimensional look.
In most of the shots, effects supervisor Steve Kullback
wanted to exaggerate the motion of the actresses floating in
the water. This floating effect had to be animated by hand.
The shots with both actresses side-by-side were especially difficult.
The girls had to be independent of one another, which would
have been easily accomplished with simple garbage mattes if
the actresses had been split apart.
However, the actresses crossed each other and broke frame. Shumway
rotoscoped where it was necessary to handle the crossing, but
the motion was limited in X and Y because of the way the actresses
broke frame. To sell the illusion, it became necessary to animate
in Z space, as well.
Since the girls are entering the air bubble to talk, they naturally
take their regulators out of their mouths. The regulators passed
from inside the bubble wall and back out again. Once the regulators
pierced the wall of the magic bubble, quick blasts of normal
air sprayed out and up towards the surface. These were added
simply by taking the bubbles shot by production, pulling a luminance
key and hand tracking a group or two for each respirator. A
little rotoscoping was needed for clean up.
The bubble surrounding the girls was supposed to be fairly large,
extending toward the camera a foot or two past the actresses.
To enhance this illusion, Shumway used the bubble's matte to
reveal the same groups of bubbles offset by a couple of frames.
This made it appear as if the normal air bubbles burst out underneath
the magic bubble, then came around and floated up out in front
and along the sides of the magic bubble. A warp was added to
enhance the illusion of depth.
The final icing on the cake was to create an airtight seal near
the actresses' waists and a subtle reflection in their face
masks. The seal was accomplished by taking the difference between
the girl's mattes and the 3D bubble mattes. The Henry has a
great emboss feature which rendered a matte that Shumway ran
a watery texture through, thus keeping the soapy-like movement
of the bubble.
The reflection in the masks needed to be so subtle that a circle
garbage matte was hand tracked for each mask. The original plates
allowed some room for error, because the rims of the mask were
metal and would reflect as well. Shumway then selected some
footage of fish on the reef, and composited it all together.
In the final shot of the sequence, Sabrina pops the bubble,
and transforms herself into an animated fish.
Modern Videofilm's Elastic Reality artist Marlan Harris
morphed Sabrina from her human form into the cartoon fish character
animation created by LightPoint Entertainment. Rick Cortes added
particle animation on a Discreet Logic Flint. The entire sequence
of five shots required more than 150 artist-hours to complete.
Sabrina Down Under was produced by Hartbreak Films and Viacom
Productions. Modern Videofilm also provides the digital effects
for the weekly Sabrina television series, which is now entering
its fourth season. Supervisor Steve Kullback and effects producer
Mark Spatny manage a team of artists that provided up to 60
effects per half-hour episode.