August 6, 2001
Barus & Holley, Rm. 190 - Eng. bldg. ground floor, 2pm.
Xavier Orriols from Barcelona is visiting us over the summer, for the second year in a row! and working on some vision problems relevant to our Digital Archaeology project. Xavier will be at the SHAPE lab until the begining of September.
Local web link : http://www.lems.brown.edu/~xo/
We address the problem of multi-frame video registration using an appearance-based framework, where linear subspace constraints are applied in terms of the appearance subspace constancy assumption. We frame the multiple-image registration in a two step iterative algorithm. First, a feature space is built through Singular Value Decomposition (SVD) of the covariance matrix of a sequence of images, where the variabilities of each frame with respect to a previously selected frame of reference are encoded. Secondly, a parametric model is introduced in order to estimate the transformation that has been produced across the sequence. This model is described in terms of a polynomial representation of the velocity field evolution, which corresponds to a parametric multi-frame optical flow estimation. The objective function to be minimized considers both issues at the same time, i.e., the appearance representation and the time evolution across the sequence. This function is the connection between the global coordinates in the subspace representation and the parametric optical flow estimates. Both minimization steps are reduced to two linear least squares sub-problems, whose solutions turn out to be in closed form for each iteration. The appearance constraints take into account all the images in a sequence in order to estimate the transformation parameters for each image. Finally, results show the extraction of 3D affine structure from multiple views depending on the analysis of the surface polynomial's degree.