Computer Graphics Laboratory ETH Zurich

ETH

Physical Face Cloning

B. Bickel, P. Kaufmann, M. Skouras, B. Thomaszewski, D. Bradley, T. Beeler, P. Jackson, S. Marschner, W. Matusik, M. Gross

Proceedings of ACM SIGGRAPH (Los Angeles, USA, August 5-9, 2012), ACM Transactions on Graphics, vol. 31, no. 4, pp. 118:1-118:10
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Abstract

We propose a complete process for designing, simulating, and fabricating synthetic skin for an animatronics character that mimics the face of a given subject and its expressions. The process starts with measuring the elastic properties of a material used to manufacture synthetic soft tissue. Given these measurements we use physicsbased simulation to predict the behavior of a face when it is driven by the underlying robotic actuation. Next, we capture 3D facial expressions for a given target subject. As the key component of our process, we present a novel optimization scheme that determines the shape of the synthetic skin as well as the actuation parameters that provide the best match to the target expressions. We demonstrate this computational skin design by physically cloning a real human face onto an animatronics figure.

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Overview

The human body consists of articulated rigid structures (bones) and soft tissue (e.g., flesh and skin). Therefore, it seems natural for animatronic characters to have a rigid articulated base and synthetic soft tissue. Many impressive characters have been created in this spirit, e.g., those in Disney World’s Hall of Presidents or “Geminoids”, androids that closely resemble human beings. However, creating such figures is still a difficult and laborintensive process requiring manual work of skilled animators, material designers, and mechanical engineers. Owing to its expressive power, the human face is probably the most challenging part in this context. An animatronic character has to produce a vast range of facial expressions, each having different deformations and wrinkles. Manually designing the shape and material properties of a single skin that is able to achieve all these targets is clearly a formidable task. The goal of this work is to automate this process, to increase the realism of the resulting character and, ultimately, to create an animatronic face that closely resembles a given human subject. In order to accomplish this task, we capitalize on recent developments from three areas in computer graphics: facial performance capture, physics-based simulation, and fabrication-oriented material design. Building on these foundations, we present a method of physical face cloning — a novel process for computational modeling, optimization and fabrication of synthetic skin for animatronic characters.

More specifically, our process comprises the following steps. First, we capture elastic material properties for a range of possible synthetic skin materials using a custom measurement system. We subsequently capture a collection of different expressions for a given target human face. As the central part of our pipeline, we then optimize the geometry of the skin and the actuation parameters of the underlying animatronics device to provide the best match to the target human face. Although our method applies quite generally to a broad range of possible animatronic devices, we validate the whole process in this paper by fabricating synthetic silicone skins for a specific articulated robot head. These skins are then animated, and the resulting shapes are compared both to the optimized model and to the real face.

Results

Figure 1: Left: photograph and scanned 3D geometry of a human face. We use a physics-based optimization process to design the geometry of a synthetic skin in order to best match given target expressions. Right: final animatronic figure with fabricated skin.

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