Fig.3 depicts a typical video sequence of an up-down gesture. This coupling is due to the different center of rotation for the head vs. the center of rotation for the cylindrical model. Even with this coupling, the estimated parameters are sufficiently distinctive to be useful in discrimination of the two nodding gestures. Given the stabilized texture map provided using the above described method, we can track nonrigid deformation of the face. However, our approach confines nonrigid motion to lie in a curved surface, rather than in a flat plane.
Facial deformations are model with image templates, using the active blobs formulation.
Each blob consists of a 2D triangular mesh with a color texture map applied, and deformation is parameterized in terms of each blob's low-order, nonrigid modes. During tracking, the rigid 3D model parameters are computed first, followed by estimation of the 2D blob deformation parameters using a robust error minimization procedure. For more details about the active blobs formulation, please see the active blobs technical report. The graph shows resulting estimates of the blob 's vertical stretching parameter. Figure 4 shows an example of using our approach.