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Sketch express: A sketching interface for facial animation
Jose Carlos Miranda, Xenxo Alvarez, Joao Orvalho, Diego Gutierrez, A. Augusto Sousa, Veronica Orvalho
The journal version of Sketch Express: strokes on a 2D canvas pose a face independently of its rig, and those poses can be stored and retargeted to other characters.
Abstract
One of the most challenging tasks for an animator is to quickly create convincing facial expressions. Finding an effective control interface to manipulate facial geometry has traditionally required experienced users (usually technical directors), who create and place the necessary animation controls. Here we present our sketching interface control system, designed to reduce the time and effort necessary to create facial animations. Inspired in the way artists draw, where simple strokes define the shape of an object, our approach allows the user to sketch such strokes either directly on the 3D mesh or on two different types of canvas: a 2D fixed canvas or more flexible 2.5D dynamic screen-aligned billboards. In all cases, the strokes do not control the geometry of the face, but the underlying animation rig instead, allowing direct manipulation of the rig elements. Additionally, we show how the strokes can be easily reused in different characters, allowing retargeting of poses on several models. We illustrate our interactive approach using varied facial models of different styles showing that first time users typically create appealing 3D poses and animations in just a few minutes. We also present in this article the results of a user study. We deploy our method in an application for an artistic purpose. Our system has also been used in a pioneer serious game context, where the goal was to teach people with Autism Spectrum Disorders (ASD) to recognize facial emotions, using real time synthesis and automatic facial expression analysis.
How to read this
- Category
- Journal extension of a sketch-based facial posing interface.
- Contributions
- A stroke-driven control system where a drawn line, not a slider, defines the shape the user wants.
- The canvas: a 2D drawing region that bounds the domain of interaction with the object being posed.
- Posing that is independent of the underlying 3D rig, so the same stroke works on differently rigged faces.
- Storage and reuse of strokes, which turns a pose into something retargetable to other characters.
- An informal user study reporting that first time users reach appealing poses within minutes.
- Context
- The journal version of miranda-sketch-express-2011, same team out of Porto with Diego Gutierrez and Augusto Sousa. The conference paper introduced strokes and canvases, this one gives the system room to be described properly and to be evaluated. It is also the paper that hands the sketch idea to Cetinaslan, who spends the next decade attaching it to blendshape rigs in cetinaslan-sketch-controllers-2015 and onwards.Builds on: Sketch Express: Facial Expressions Made Easy
- Correctness
- The user study is explicitly informal, so treat the speed claims as encouraging rather than established. The stronger claim, rig independence, is the one to interrogate: it holds because strokes act on an implicit volume rather than on rig controls, but that also means the system cannot exploit a good rig when one exists. Check how the examples handle faces whose stylisation is far from the ones shown.
- Clarity
- Very readable. The metaphor does most of the explaining and the figures carry the argument, which is exactly what you want from an interface paper.
- How to read it
- First pass: abstract, the canvas figure, the results gallery. Second pass: the stroke to deformation mapping, and the study section with its limitations in view. Third pass: skip unless you are building an interface, in which case compare it side by side with miranda-sketch-express-2011 to see what the extra pages bought.
Builds on
Built upon by
Nothing yet.
Related work
- Sketch Express: Facial Expressions Made Easy 2011 / Eurographics
- Direct manipulation of blendshapes using a sketch-based interface 2018 / Web3D
- Sketch-Based Controllers for Blendshape Facial Animation 2015 / Eurographics
- Sketching Manipulators for Localized Blendshape Editing 2020 / GMOD
Keywords
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