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Step 2: Animation of the Face using the Jaw.

A surprising amount can be accomplished simply by attaching (enveloping) the face to the jaw bone. Rather than using the several hundred control points present in the final surface, and thus having to resolve those envelopes with any other facial actions, the jaw controls the shape of the coarsest resolution of the surface, freeing other actions to work on the details of the face.

Figure 4. Surface Attachments.

The basis of animating with multi-resolutions surfaces is to use a "top-down" approach, animating the coarsest level of detail first and adding additional effects to the details later. To animate the jaw, 12 control points at Level 0 were attached to the jaw bone (enveloped with weight 1 in SoftImage parlance). These points are high-lighted in red in Figure 4.

Figure 5. Opening the Jaw.

When the jaw is rotated, Level 0 acts appropriately deforming the surface as would a normal b-spline of the same resolution and shape. But with a hierarchical spline surface details (in this case all the facial features) are carried along with the Level 0 deformation with very little distortion.

Figure 6. Level 1 with the jaw open.

Figure 6 simply displays the results of the Level 0 deformation on Level 1 of the model, Figure 7 is Level 2 and Figure 8 shows the entire model with all levels.

  Figure 7. Level 2.

 Figure 8. All Levels.

Note that this effect is not the same as you would get by attaching/enveloping all the control points of a traditional B-spline.

 Figure 10. Jaw Closed

The following figures show the results of moving the jaw around. No other effects besides the Level 0 attachments/enveloping was used.

 Figure 11. Jaw Open

 Figure 12: Jaw open & twisted

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