The design framework was a powerful aid for structuring design
options for the novel multi-touch animation system presented
above. We have also used it in the design of a performance-based
animation timing technique and are employing it in ongoing projects. A design framework as presented
in this paper cannot be directly evaluated. Its usefulness and
appropriateness is rather proven indirectly through evaluations
of prototypical systems built on its theoretical foundation. For this
reason we will next summarize the evaluation of the multi-touch
animation system.
We evaluated the resulting system in an informal user study.
Aspects of interest were the reception and use of single- and
multi-track capture and camera controls, specifically in how far
two-handed interaction strategies would be employed. Since the
direct animation system has a high novelty and is still at prototype
stage, a formative evaluation was chosen in order to guide further
research. Formative evaluations are common in research and
development of 3D user interfaces [4]. Six right-handed individuals
aged between 23 and 31 years, four male, two female, took part in
our study. All came from a computer science and/or media production
background. Two of these judged their skill level as frequent
users of animation software, one as an occasional user and three
as rarely using such software. In session of about 30 min, the users
did free animations of a stylized human puppet. An articulated
mannequin was rigged with seven handles that provided puppetry
controls (three bones for control of the body and four inverse kinematic
handlers for hand and foot end effectors). The inverse kinematics
handlers allowed expressive control of the multi-joint limbs
while keeping complexity at a minimum. The goal was to explore
what own animation goals users would come up with given the
digital puppet. The study ran the prototype on a rear-projected
horizontal interactive tabletop employing the diffuse illumination
technique with a height of 90 cm, screen diagonal of 52 inch and
a resolution of 1280 800 pixels.
The results of the study revealed that participants took to the
controls easily. Most stated that they enjoyed using our system.
The performance control interface was straightforward for initial
animations. Multi-track animation was mainly used to animate
separate features in multiple passes, less to adjust existing animation.
The more complex additive mapping was hardly used and
met with initial confusion, although explanation and experimenting
usually solved this. The view controls were quickly understood
and were used without difficulty. The most commonly used camera
operation was orbit. As all participants were familiar with
the timeline metaphor they had no problems understanding it.
Most subjects easily employed the absolute positioning of the
playhead to jump to a frame and to scrub along the timeline to
review the animation they had created. One participant used the
timeline for a method of animation somewhere between performance
and frame-based animation: using the left hand for playhead
and the right for pose control, he exerted a fast, efficient
pose-to-pose animation style. Five out of six participants manifested
asymmetric bimanual styles of interaction. An emergent
strategy of half of our study’s participants was to dedicate the left
hand for view or time controls and the right for capture. Further,
one participant controlled two puppet features simultaneously.
Three used their left hand to attach the view to the mannequin
for animating its limbs once they had created animation for the
root bone. The benefit of locking the view to a frame of reference
in this way seemed immediately apparent to them, and was
greeted with enthusiasm in two cases.
Given the short timeframe and lack of experience in performance
animation, participants were able to create surprisingly
refined character motion. Four were able to create expressive character
animations within the short timeframe of 10 min in the free
animation task. These were a walk, jump and squat motions and
dance moves.
Inexperienced users had a harder time to comprehend spatial
relationships, while those with more experience in 3D animation
notably picked up controls more fluently. This comes as no surprise,
as using and controlling software takes time and practice,
regardless of interface. For novice and casual users, our 2DOF strategy
seems appropriate, since it constrains manipulation by the
depth dimension. However, the interface might need improvement
visualizing these constraints and giving more hints on depth cues.