Game Development Reference
In-Depth Information
processing, analysis tasks, noise suppression, feature extraction, pattern recog-
nition, etc. In Serra (1982, 1988), the authors explain in depth how to take
advantage of these techniques for the processing of images. This set of tools
gives the means to develop algorithms to efficiently detect edges and specific
areas of the face.
Deformable models
A deformable model is a group of parametric curves with which we try to
approximate the contours of an image and the behavior of the objects present on
it. The advantages of a deformable template are its computational simplicity and
the few number of parameters needed to describe different shapes. Unfortu-
nately, since a template is generally made specifically for a given shape, we need
to redefine the rules of parameter variation so that the model follows the right
contours. Since they have a difficult adaptation to unexpected shapes, their
biggest disadvantage is dealing with noisy images. The diversification of
solutions is well seen in the literature, where we can find as many different
models as articles treating the subject (Yuille, 1991). Some of the most common
models are:
•
Elliptical: circles and ellipsoids can model the eyes (Holbert & Dugelay,
1995).
•
Quadratic: parabolic curves are often used to model the lips (Leroy &
Herlin, 1995).
•
Splines: to develop more complex models, splines are an option. They have
already been used to characterize mouth expressions (Moses, Reynard &
Blake, 1995).
Post-Processing Techniques and Their
Related Mathematical Tools
To recreate motion on synthesized 3D-models, it is necessary to relate the
analyzed information to the Facial Action Units (AUs) or Facial Animation
Parameters (FAPs). If motion is not derived heuristically from the image
processing results themselves, the derivation of motion is sometimes helped by
the iterative feedback synthesis of the motion actions on the model. As explained
by Eisert and Girod (1998), we must find some mathematical solution to tie
analysis to synthesis.
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