This article summarizes the third day of the ICCV 2015 conference, the International Conference on Computer Vision. A summary of the first day and second day is also available.
Registering Images to Untextured Geometry Using Average Shading Gradients
By Tobias Ploetz and Stefan Roth.
This work considers the difficult problem of aligning an untextured 3D surface to a real image of the same object, a challenging problem because of the absence and presence of edges depending on texture and light.
The authors propose an alignment procedure that uses efficiently computable average shading gradient images that capture expected visible edges due to shadows despite unknown light direction.
Paper.
Robust Nonrigid Registration by Convex Optimization
By Qifeng Chen and Vladlen Koltun.
The authors consider the problem of aligning two 3D shapes to each other, where each shape may be corrupted by missing surfaces (non water-tight surfaces) and undergo severe nonrigid deformations. Previous work has proposed to minimize a specific geodesic distortion measure over suitable classes of continuous transformations, however, this yields difficult non-convex optimization problems.
Because the distortion measure makes sense this work proposes a way to approximate while simultaneously convexifying the problem. This is achieved by representing the transformation nonparametrically through correspondences on randomly sampled points. While the original problem was continuous and non-convex, now it is a discrete energy minimization problem that can be approximately solved using a standard LP-based relaxation approach, where the authors use TRW-S.
What is surprising is how much the results improve on benchmark data sets; the error is reduced by a factor of three compared to strong baseline methods.
Paper.