We present a new interactive automatic skinning method,
which produces plausible skin elasticity,
and improves stability over earlier methods such as implicit skinning.
The new technique also allows for more complex shape motions including large angle joint bends,
and handle skin contact and muscles bulges.
Popular approaches like dual quaternion skinning is very fast to compute,
but it introduces unwanted bulges, self-intersections, and large parametric distortions.
The recent implicit skinning approach
fixes the common twisting and bending artifacts
while introducing plausible skin contacts in real time.
Unfortunately, parametric distortions are still evident in extreme bends
In contrast, our technique twists and bends robustly
while producing skin contacts, controls parametric distortions,
and also includes a global elasticity model.
In all the following results: we use automatic skinning weights
computed with heat diffusion.
We first show dual quaternion skinning with large self-intersecting areas,
here between the arm the torso.
Next implicit skinning performs skin contacts,
but is unable to correct the skin crease at the shoulders.
In addition, the effect of skin elasticity is limited
and only visible in the upper part of the back.
Our method avoids the crease and produces the effect of global skin elasticity.
Notice how the skin moves in the lower part of the back.
When leaning sideways, dual quaternions exhibit a crease in the torso
together with an unwanted loss of volume.
Implicit skinning compensates for this loss,
but also produces the unwanted crease.
Our method, automatically distributes the vertices over the implicit skin.
The crease disappears
and the global elasticity effect can be seen on the belly.
Our approach improves stability and robustness in two ways.
Firstly, for a large bend,
dual quaternions typically produce self-intersections.
Notice how the mesh is stretched at the elbow.
Implicit skinning is also unable to correct the meshes distortions,
and when self-intersections of dual quaternions are too deep,
the projection on the implicit surface fails to produce the proper skin contact
Unlike implicit skinning,
our method is free from these problems
as we don't rely on an initial dual quaternion approximation.
Secondly, implicit skinning generates discontinuous gradient in the scalar field
at the composition stage,
this can lead to flickering artifacts seen below the character's breast.
Our new composition operators produces smooth scalar field
and avoid this problem.
Notice also the belly button stretch produced by the global skin elasticity model.
In the animation of the hand, dual quaternions introduce the self-intersection problem.
Implicit skinning does not correct this due to gradient discontinuities in the scalar field.
Our method doesn't exhibit this creasing or flickering artifacts.
For detailed characters dual quaternions do not produce plausible results.
Implicit skinning goes a step further toward realism,
but restricts the size of the bending angle due to problems with the generated implicit field.
Our approach allows large bending angles
so that an artist using this technique can add primitives
representing muscles without worrying about intersection problems.
In the last example,
we show the overall robustness of our method
on a fully skinned armadillo model with a complex animation.