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Expression Cloning. Jung-yong Noh Ulrich Neumann Siggraph01. Introduction (1/2). What is Expression Cloning? Allow animations to be easily retargeted to new models Why Expression Cloning? Easily create facial animations for character models Provide an alternative from scratch.

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Expression cloning l.jpg

Expression Cloning

Jung-yong Noh Ulrich Neumann

Siggraph01


Introduction 1 2 l.jpg
Introduction (1/2)

  • What is Expression Cloning?

    • Allow animations to be easily retargeted to new models

  • Why Expression Cloning?

    • Easily create facial animations for character models

    • Provide an alternative from scratch


Introduction 2 2 l.jpg
Introduction (2/2)

  • How to do Expression Cloning?

    • Transfer vertex motion vectors from a source face model to a target model

      1. Determine surface points correspondence

      2. Transfer motion vectors


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Related works (1/4)

  • Two kinds of facial animation approaches

    1. Physical behaviors of the bone and muscle structures

A Muscle Model for Animating Three-Dimensional Facial Expression, K. Waters et al [31]


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Related works (2/4)

  • Two kinds of approaches

    2. Smooth surface deformation

     Animation do not simply transfer between models

Making Faces, H. Malvar et al [31]


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Related works (3/4)

  • Reusing data for new models

    • Vector based muscle models

      • Placing heuristic muscles under the surface of the face

      • Repeat for each new model

    • A parametric approach

      • Associating the motion of a group of vertices to a specific parameter

      • Manual association must be repeated for models


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Related works (4/4)

  • The goal of this paper

    • Reusing motion data to produce facial animations

      • Same qualities

      • Easily transform

      • Control varied target models from one generic model

  • Similar work

    • Performance driven facial animation, MPEG-4

      • Tracking a live actor; 84 feature points


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Expression Cloning (1/11)

Two steps:

1. Dense surface correspondences

2. Animation with motion vectors


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Expression Cloning (2/11)

  • Dense surface correspondences

    • Determine which surface points in the target correspond to vertices in the source model

      • Different number of vertices or connectivity

      • Small set of initial correspondences to establish an approximate relationship


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Expression Cloning(3/11)

  • Dense surface correspondences

    • Radial Basis Functions (RBF)

      • Roughly project vertices in the source model onto the target model

    • Cylindrical Projections


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Expression Cloning (4/11)

  • Dense surface correspondences


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Expression Cloning (5/11)

  • Animation with Motion Vectors

    • Displace each target vertex to match the motion of a corresponding source surface point.

      • Need Dense source motion vectors, linear interpolation

      • Direction and magnitude of a motion vector must be altered and scaled


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Expression Cloning (6/11)

  • Animation with Motion Vectors

    2.1 Motion Vector Direction Adjustment

    2.2 Motion Vector Magnitude Adjustment


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Expression Cloning (7/11)

  • Direction Adjustment


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Expression Cloning (8/11)

  • Magnitude Adjustment


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Expression Cloning (9/11)

  • Direction Adjustment & Magnitude Adjustment

▪ Local bounding box (BB), scale and rotate▪ limit by a global threshold

▪ m : motion vector


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Expression Cloning (10/11)

  • Lip contact line

    • Models have lips that touch at a contact line

    • Lower lip vertices may be controlled by upper lip triangle

    • Solve:

      • Include all the source-model lip contact line vertices for the RBF morphing step

      • Completely align the lip contact lines of the two models


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Expression Cloning (11/11)

  • Automated Correspondence Selection

    • A small set of correspondences is needed for the RBF morphing

    • 15 heuristic rules when applied to human faces


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Results

  • Animation can be created by motion capture data

  • Wide variety of target models


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Conclusion

  • Expression cloning

    • Use high-quality dense 3D data in source model animations

    • Produce animations of different models with similar expressions

    • The method is fast and produces real time animations.


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Future Works

  • Stick figures and cartoons

    • Use sparse source data without loss of expressive animation quality

  • Control knobs

    • To amplify or reduce a certain expression

  • Tongue and teeth model


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