Real-time Skeletal Skinning with Optimized Centers of Rotation Binh Huy Le * Jessica K. Hodgins † Disney Research Figure 1: The deformations created by our new direct skinning method on several key poses of an animation. With the same setup, our method reduces the bulging artifact of dual quaternion skinning (DQS) on the chest and the candy wrapper artifact of linear blend skinning (LBS) on the shoulder of the model. The artifacts are indicated by red arrows. Abstract Skinning algorithms that work across a broad range of character de- signs and poses are crucial to creating compelling animations. Cur- rently, linear blend skinning (LBS) and dual quaternion skinning (DQS) are the most widely used, especially for real-time applica- tions. Both techniques are efficient to compute and are effective for many purposes. However, they also have many well-known arti- facts, such as collapsing elbows, candy wrapper twists, and bulging around the joints. Due to the popularity of LBS and DQS, it would be of great benefit to reduce these artifacts without changing the an- imation pipeline or increasing the computational cost significantly. In this paper, we introduce a new direct skinning method that ad- dresses this problem. Our key idea is to pre-compute the optimized center of rotation for each vertex from the rest pose and skinning weights. At runtime, these centers of rotation are used to interpo- late the rigid transformation for each vertex. Compared to other direct skinning methods, our method significantly reduces the ar- tifacts of LBS and DQS while maintaining real-time performance and backwards compatibility with the animation pipeline. Keywords: skinning, skeletal animation, blending, real-time ani- mation Concepts: •Computing methodologies → Animation; * e-mail: binh.le@disneyresearch.com † e-mail: jkh@disneyresearch.com Permission to make digital or hard copies of all or part of this work for per- sonal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than the author(s) must be honored. Abstract- ing with credit is permitted. To copy otherwise, or republish, to post on 1 Introduction Good skinning algorithms are of fundamental importance for ani- mating characters, such as humans or animals. Skinning methods must generate high-quality, detailed deformations around the joints of the characters from a small set of controllers. Among the many available skinning methods, skeletal-based algorithms are the most widely used. Generally, they employ a simplified version of the anatomical skeleton as the controller. The character is deformed by rotating the bones around its joints. Each bone propagates its transformation to the limb that it supports. The skin deformation typically appears near the joints where an area of the surface is in- fluenced by the transformations of two or more bones. Two skeletal-based models, linear blend skinning (LBS) [Magnenat-Thalmann et al. 1988] and dual quater- nion skinning (DQS) [Kavan et al. 2008], are implemented in most game engines, virtual reality engines, and 3D animation software. Both LBS and DQS are direct methods with closed-form solutions where each vertex transformation is computed as a weighted-blend of bone transformations. Both LBS and DQS only require users to provide per-vertex skinning weights and per-frame bone transformations. These inputs are intuitive and users can easily manipulate the weights using painting tools. While the calculations of the deformations with LBS and DQS are different, their implementations are very similar and the most effective ways of calculating the vertex transformations utilize GPU vertex shaders. Due to this simplicity and efficiency, LBS servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from permissions@acm.org. c ⃝ 2016 Copyright held by the owner/author(s). Publication rights licensed to ACM. SIGGRAPH ’16 Technical Paper,, July 24 - 28, 2016, Anaheim, CA, ISBN: 978-1-4503-4279-7/16/07 DOI: http://dx.doi.org/10.1145/2897824.2925959