max planck institut
informatik
informatik
Our research focuses at anatomically correct modeling and physically based animation of human faces and bodies. To this end, we have developed MEDUSA and LEONARDO, two systems for modeling and animation of faces and bodies, respectively. Both of these systems include tools and techniques for a variety of sub-tasks that have to be handled in order to generate photorealistic facial and full-body animations in real-time on standard PC hardware. Both MEDUSA and LEONARDO are used for research and education purposes.
Investigators: Irene Albrecht and Jörg Haber
Facial reconstruction for postmortem identification of humans from their skeletal remains is a challenging and fascinating part of forensic art. The former look of a face can be approximated by predicting and modeling the layers of tissue on the skull. This work is as of today carried out solely by physical sculpting with clay, where experienced artists invest up to hundreds of hours to craft a reconstructed face model [Tay01]. Remarkably, one of the most popular tissue reconstruction methods bears many resemblances with surface fitting techniques used in computer graphics, thus suggesting the possibility of a transfer of the manual approach to the computer. In [KHS03], we presented a facial reconstruction approach that fits an anatomy-based virtual head model, incorporating skin and muscles, to a scanned skull using statistical data on skull/tissue relationships, see Figure 0.1. The approach has many advantages over the traditional process: a reconstruction can be completed in about an hour from acquired skull data; also, variations such as a slender or a more obese build of the modeled individual are easily created. Last not least, by matching not only skin geometry but also virtual muscle layers, an animatable head model is generated that can be used to form facial expressions beyond the neutral face typically used in physical reconstructions.
|
In [ASHS05], we introduced an algorithm for generating facial expressions for a continuum of pure and mixed emotions of varying intensity. Based on the observation that in natural interaction among humans, shades of emotion are much more frequently encountered than expressions of basic emotions, a method to generate more than Ekman's six basic emotions (joy, anger, fear, sadness, disgust and surprise) is required. To this end, we have adapted the algorithm proposed by Tsapatsoulis et al. [TRK+02] to be applicable to our MEDUSA system and a single, integrated emotion model. We combined MEDUSA with an equally flexible and expressive text-to-speech synthesis system, based upon the same emotion model, to form a talking head capable of expressing non-basic emotions of varying intensities.
In [FHS04], we presented a versatile language for specifying facial animations. The language MIMIC can be used together with any facial animation system that employs animation parameters varying over time to control the animation. In addition to the automatic alignment of individual actions, the user can fine-tune the temporal alignment of actions relatively to each other. A set of pre-defined functions can be used to control oscillatory behavior of actions. Temporal constraints are resolved automatically by the MIMIC compiler.
To equip our head models with hair, we proposed a hair model together with rendering algorithms suitable for real-time rendering [KHS04]. In our approach, we take into account the major lighting factors contributing to a realistic appearance of human hair: anisotropic reflection and self-shadowing. To deal with the geometric complexity of human hair, we combine single hair fibers into hair wisps, which are represented by textured triangle strips. Our rendering algorithms use OpenGL extensions to achieve real-time performance on recent commodity graphics boards, see Figure 0.2.
|
Investigators: Irene Albrecht, Mardé Greeff, and Jörg Haber
The human hand is a masterpiece of mechanical complexity, able to perform fine motor manipulations and powerful work alike. Designing an animatable human hand model that features the abilities of the archetype created by Nature requires a great deal of anatomical detail to be modeled. In [AHS03], we presented a human hand model with underlying anatomical structure (see Figure 0.3). Animation of the hand model is controlled by muscle contraction values. We employ a physically based hybrid muscle model to convert these contraction values into movement of skin and bones. Pseudo muscles directly control the rotation of bones based on anatomical data and mechanical laws, while geometric muscles deform the skin tissue using a mass-spring system. Thus, resulting animations automatically exhibit anatomically and physically correct finger movements and skin deformations. In addition, we presented a deformation technique to create individual hand models from photographs. A radial basis warping function is set up from the correspondence of feature points and applied to the complete structure of the reference hand model, making the deformed hand model instantly animatable. We have successfully used our hand model in another project [TAH+04], where we capture the movement of a baseball and the pitcher's hand using stroboscope lighting and regular still cameras as described in the Section "Capturing Rapid Motion with Regular Still Cameras".
|
Inverse kinematics is commonly applied to compute the resulting movement of an avatar for a prescribed target pose. The motion path computed by inverse kinematics, however, often differs from the expected or desired result due to an underconstrained parameter space of the degrees-of-freedom of all joints. In such cases, it is necessary to introduce additional constraints, for instance by locking a joint's position and/or rotation. In [GHS05], we described a method to fix a joint in terms of position and/or rotation and explained how to incorporate these constraints into the inverse kinematics solution.
