Automatic 3D Face Model Adaptation with Two Complexity Modes for Visual Communication - 3D Modeling and Animation: Synthesis and Analysis Techniques for the Human Body - page 304

thickness and opening heights (Kampmann & Zhang, 1998). In the following,
only selection of an appropriate mouth model and estimation of mouth opening
heights and lip thickness are addressed in detail.

Automatic Selection of 2D Mouth Models
To estimate the 2D mouth features, an appropriate 2D mouth model has to be
automatically selected. To do this, it must be known whether the mouth is open
or not. Compared with a closed mouth, which consists of three lip contours, an
open mouth has an additional fourth lip contour.
The mouth area M is determined by means of the mouth width L , the distance
between the mouth corner positions (ref. Figure 6). Here, the area of the lower
lip with the size of L × 0 5 L is supposed to be larger than the area of the upper

lip with the size of , because the lower lip has larger movement than the

upper lip. Since a lip contour is labeled with high luminance variation, edge
strength (image gradient) g y ( x,y ) in the mouth area is computed using a
morphologic edge operator. It is further binarized with a threshold and thinned.
The lines produced using these methods are the candidates for the possible lip
contours. Finally, an appropriate 2D mouth model is automatically selected by
comparing a number of possible positions for the lip contours above and below
the line l , connecting both mouth corner positions.

L × 0 3 L

Estimation of the Thickness and the Opening Heights of Lips
After the appropriate 2D mouth model has been selected, the parameters of the
mouth model are estimated by minimization of cost functions. Since the mouth

Figure 6. Position detection of candidates for lip contours for 2D mouth
model.