Tuesday, March 30, 2010

Simplified facial animation control utilizing novel input devices: a comparative study

Nikolaus Bee University of Augsburg, Augsburg, Germany
Bernhard Falk University of Augsburg, Augsburg, Germany
Elisabeth André University of Augsburg, Augsburg, Germany

Paper Link:

Animating facial expressions can be difficult due to the fact that most facial expressions involve the simultaneous movement of different muscle groups.
Graphic designers can usually only move one certain muscle group through a bar slider and a mouse however this makes good facial animation difficult.
So the team used a gamepad and data gloves that would allow parallel editing using several different mapping schemes.

The model for facial manipulation that the team used was the "Alfred" (Facial Action Coding System) FACS based model with 23 action units.
FACS was used for Gollum in Lord of the Rings. King Kong, and Half-Life 2.

For the gamepad the team chose the XBOX 360 controller because it was ergonomic, cheap, familiar, and can be easily connected to a Windows PC.
The 360 controller offered 2 analog sticks and 2 analog triggers.
The sticks offer x and y axis control with both negative and positive values allowing for 4 different parameters to be controlled by one stick.
The other stick control used a circular polar coordinate based control.

The digital buttons and directional pad was used for other control functions like switching the current setting and action unit mappings.
Mapping of the controls for the gamepad included three settings:
1) Upper face with 7 action units
2) Lower face 1
2) Lower face 2 - Inner lips

For the data glove, the team chose the "P5 Glove" which was originally designed for gaming, making it cheap and widespread. The data glove can provide for 5 simultaneous movements. The data gloves can register one dimensional finger bends and the orientation and positions of the hand making it a near perfect candidate to replace the traditional slider. The P5 glove has the following features:
• absolute position (x,y,z), relative position (x,y,z), and rotation
(yaw, pitch, roll)
• finger bend
• three additional digital buttons
Mapping of the data glove used 6 settings:
1) Brows - 3 AUs
2) Lids - 3 AUs
3) Cheek and Nose - 3 AUs
4) Corners of the Mouth - 4 AUs
5) Chin and Inner Lips - 4 AUs
6) Lips - 3 AUs
Selection of the 6 settings was done by moving the glove horizontally

After running a correlation analysis of Action Units to expressions
of joy, anger, fear, sadness, disgust, and surprise and finding the frequency of use of certain actions to each emotion, the team devised a context-based control mapping where higher used AUs to an emotion mode.

Professional Study:
They introduced the devices by coaching
and listened to the game developers think aloud.

Directly mapped gamepad interface: Liked
Context mapped gamepad interface: difficult to orient and get familiar, less control

Data glove: less familiar, not accurate, physically tiring, noisy, selecting a setting was difficult.

Formal User Study:
1) How users get along with novel input versus sliders
2) Enjoyment?
3) Assessment of technical features:

5 point scale, 17 users age 20 to 40, 76% students
training phase - mess around with the device
modeling phase - recreate a photo expression

Accuracy Speed Satisfaction of expression
Gamepad 4.26 148.06 s 3.63
sliders 4.56 168.29 s 3.84
dataglove 4.94 263.31 s 3.30

Gamepad - best mean scores, reduced production time, no loss of quality, 49% preferred

Data glove - can focus on work, slower, low quality, low comfort, insufficient accuracy, 24% preferred

Sliders - 27% preferred, have to shift focus, accurate, reasonable satsifaction
Interaction experience

My Spill:
I was surprised to learn that gamepads aren't already the standard method of input in facial design. It seems like the ergonomic design and multiple functions would lend itself to that role and the user study seems to reflect that.

That said, I wish the data glove would have produced some better results, it seems like you could make facial animations quickly with 5 different levels of control. Maybe they needed a better mapping scheme for it.

I think using sliders sounds boring and too difficult given that you can only control one thing at a time.

I'd like to see more work on the power glove to make it as efficient and enjoyable as the other two methods.

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