Cancelling Ambient Occlusion
Tracking deforming surfaces is an important sub-problem for many scenarios, such as facial performance capture. When a surface is deformed, the changing shape can cause a change in appearance (shading), e.g. when forming wrinkles. These appearance changes pose problems for most existing tracking methods, as they rely on the local appearance to be constant.
We present a general technique for improving space-time reconstructions of deforming surfaces, which are captured in an video-based reconstruction scenario under uniform illumination. Our approach simultaneously improves both the acquired shape as well as the tracked motion of the deforming surface. The method is based on factoring out surface shading, computed by a fast approximation to global illumination called ambient occlusion. We show that once local surface shading has been removed, optical flow can be computed much more robustly and with higher accuracy. While cancelling the local shading, we also optimize the surface shape to minimize the residual between the ambient occlusion of the 3D geometry and that of the image, yielding more accurate surface details in the reconstruction. Our enhancement is independent of the actual space-time reconstruction algorithm. We experimentally measure the quantitative improvements produced by our algorithm using a synthetic example of deforming skin, where ground truth shape and motion is available. We further demonstrate our enhancement on a real-world sequence of human face reconstruction