Facial Motion Capture
More for nostalgia than any other reason, we have
included these pictures to illustrate just how far we have come
from the early days for "mechanical capture". Above is
one of the first motion capture rigs we built for Jim Henson's Creature
A combination of rotary potentiometers, LVDTs (Linear
Variable Diferential Transformer), and Infra-Red transmitter/receiver
modules enabled facial expressions to be converted into electronic
signals for driving animatronic robots in real time.
Part of the main design concern was ambient background
light levels that can cause interference to Infra-Red systems. This
has the effect of distorting the animatronic control signals as
the sun came out from behind a cloud - basically messing up the
characters expressions. In this version we cancelled out
any background light, and successfully used it under varying sun
and strobe lighting conditions.
Facial capture for Lost
In Space feature film
A few years down the line we got our hands on one
of the first Vicon 370 optical mocap rigs, and started to capture
facial expressions using reflective markers stuck onto the actors
face. Whist in the early day this was not real time, it did give
us more detailed information than any electro-mechanical system.
As computer processing power grew during the 90s, and mocap rigs
improved, we were able to increase the resolution and accuracy of
the system, and are now able to drive both mechanical and computer
graphic creature faces in real time to sub-millimetre precision.
For all of the advantages of highly accurate real
time facial capture with all of its lip-synch capabilities, there
is one point that should not be forgotten. For many dynamic creature
expressions it is often preferable to use hand control inputs as
puppetry devices or key frame techniques rather than recording directly
off a performers face.
Hand controls can give the puppeteer more control
and enable exaggerated expressions that are ideal of an non human
creature. Examples of mixing full-body optical mocap and hand controls
for facial animation can be seen in movies about HDPS(TM)
(Henson Digital Performance Studio).
Facial capture and hand controls are mainy used for
live performances and some video game productions, however for high
quality feature film work, the majority of characters facial movements
are still key framed for finer control. Often human movement is
not aesthetically desired, particularly for non human characters,
and a more stylised performance is best generated by other techniques.
In conclusion, choosing the right technology for the
right situation is critical for controlling digital and animatronic
creatures in the sytle that you desire.