Differential Blending for Expressive Sketch-Based Posing

Project Members

Cengiz Ă–ztireli (ETH Zurich)
Ilya Baran (Disney Research Zurich)
Tiberiu Popa (ETH Zurich)
Boris Dalstein (Disney Research Zurich)
Bob Sumner (Disney Research Zurich)
Markus Gross (Disney Research Zurich)

PROJECT_ExpressiveSketchBasedPosing_sca2013_teaser

Caricatured poses and expressive movement are the hallmark of hand-drawn animation, where pencil and paper afford the artist full creative freedom when crafting the shape and movement of animated characters. In three-dimensional animation, however, highly expressive and caricatured poses are more difficult to achieve, because the artist interacts with the character indirectly via the character’s rigging controls. As a result, expressive poses that come naturally from the fluid interaction of paper and pencil can be cumbersome or impossible to achieve using modern 3D animation tools.

Our research addresses these shortcomings in 3D animation by proposing a novel blending method for skeletal deformations and illustrating how it can be used to transfer the concept of “\emph{line-of-action}” curves from 2D hand-drawn animation for creating highly expressive poses with intuitive sketch-based controls in 3D animation. In 2D animation, these curves serve as a guide to convey the composition, balance, energy, and dynamics of the character’s pose. By interpreting these curves for 3D skeletal deformations, our system allows fast and intuitive creation of highly expressive poses that are notoriously difficult to obtain with complex classical rigs.

The core technical challenge of developing such a system lies in blending skeletal transformations. Because highly expressive poses involve large bends and twists, the rigging system is forced to blend large, disparate rotations in complex regions such as the shoulder where vertices are influenced by multiple portions of the skeleton. Due to ambiguities inherent in the representation of rotations, blending algorithms used by existing rigging systems fail to give smooth and intuitive results in this case. To solve these problems, we propose a new blending technique specifically designed for large and disparate transformations, as our main contribution. Our “\emph{differential blending}” method represents all transformations in a differential manner and computes averages of the differential transformations, which are then composed to get the final blended transformation.

Presented at the ACM Symposium on Computer Animation (SCA) 2013 – July 19-21, 2013 – Anaheim, CA

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