A group of Carnegie Mellon
researchers, in association with Disney Research of Pittsburgh, are bringing
animations closer to reality by modeling accurate eye blinks.

Conventional systems that model eye blinks have always assumed them to be symmetric. In other words,
during an eye blink, a person’s eyelids move down at the same rate that they
move back up. While this may be a rational assumption to make, researchers’
high speed cameras a slightly different story: real human eyelids go down
quickly during an eye blink, followed by a more gradual opening back up.

While it may not be apparent what difference this minor detail makes, it turns out this is a huge matter of
importance for animators striving for realism, especially in big-budget
feature-length animated films. Laura Trutoiu, a Ph.D. student in Carnegie
Mellon’s Robotics Institute involved in this research, shed some light on why
this is the case. 

“Because we see so many eye blinks daily, we’re pretty good at intrinsically ‘understanding’ a good eye
blink,” Trutoiu explained. “So even though it’s very hard for a person to tell
you what is a good eye blink, when you actually see something that’s wrong with
one, that’s when you can tell.”

To further illustrate her
point, Trutoiu pointed to an interesting study her team conducted. In this
study, participants were asked to view over 300 types of blink animations and
rate the “naturalness” of each one along the way. In spite of the overall tediousness
of the process, all of the participants rated the blinks resembling real data
significantly higher than those with simple, symmetric algorithms.

“People might not be able to describe what’s different about them, but they do recognize them as different,”
summarized Liz Carter, a research associate in the Robotics Institute also
involved with the blinking studies.

There is a lot more to the team’s research than just the speed at which the eye blinks. “There are other
interesting points, like how the lower eyelid moves, how the eyes close, and so
on,” said Trutoiu.

Taking all of these and other factors into consideration, the research team then utilized tracking software
to capture real human eye motions, and generated a data set that described the
motions that could be fed into a matrix. Principal Component Analysis (PCA), a
way to highlight the important features of arbitrary input information, was
then applied to the old data to generate new types of realistic blinking
motions.

“Using PCA to lower the dimensionality of the data can also bring out patterns in the original data that would
otherwise be harder to detect,” Trutoiu noted. 
“In the case of eye blinks, a
150-points time series can be represented with 3–5 principal components.” In
other words, PCA takes the plethora of information about eye blink motions, and
simplifies that information to its most basic form.

Animating realistic eye blinks on three-dimensional models is a great way for animators to add more
realism to their work, but they also have to be wary of falling into a hidden
trap.

“So, basically, as robots or animated characters become more realistic, you like them up to a certain point,”
Carter said. “[After this point], it becomes really creepy and you don’t like
them at all,” she explained.

“It’s the uncanny valley hypothesis,” Trutoiu added, referring to the term coined by robotics researcher
Masahiro Mori in 1970.

“It’s hard to say how important eye blinks are overall, but if you want realistic character
animations, you have to get everything right. If that means raising the
eyebrows or the eye blinks correctly, it’s going to make a huge difference. If
you mess up one of those tiny, tiny things, you’ve just ruined the whole image.”

Readers who have seen the 2007 CGI film Beowulf, may be familiar with this effect already. It has
been noted by some as lacking the “true spark of life” in its animated moving
faces, despite its ultra-realistic attempts. So if you’ve ever been unnerved by
that “almost real but not quite” look in Beowulf or other
ultra-realistic animations, the uncanny valley hypothesis might have had
something to do with it.

The researchers published their study in the Association for Computing Machinery Transactions on Applied
Perception, and gave a talk on their findings at the Symposium on Applied
Perception in Graphics and Visualization in Toulouse, France, earlier this
year.

Source

The Tartan: Carnegie Mellon
student newspaper