Generalized Image Acquisition and Analysis

Discovering the Structure of a Planar Mirror System from Multiple Observations of a Single Point

We investigate the problem of identifying the position of a viewer inside a room of planar mirrors with unknown geometry in conjunction with the room’s shape parameters. We consider the observations to consist of angularly resolved depth measurements of a single scene point that is being observed via many multi-bounce interactions with the specular room geometry. Applications of this problem statement include areas such as calibration, acoustic echo cancelation and time-of-flight imaging. We theoretically analyze the problem and derive sufficient conditions for a combination of convex room geometry, observer, and scene point to be reconstructable. The resulting constructive algorithm is exponential in nature and, therefore, not directly applicable to practical scenarios. To counter the situation, we propose theoretically devised geo- metric constraints that enable an efficient pruning of the solution space and develop a heuristic randomized search algorithm that uses these constraints to obtain an effective solution. We demon- strate the effectiveness of our algorithm on extensive simulations as well as in a challenging real-world calibration scenario.


Synchronization and Rolling Shutter Compensation for Consumer Video Camera Arrays

Derek Bradley, Bradley Atcheson, Ivo Ihrke, Wolfgang Heidrich
In: Proceedings of PROCAMS 2009 (2nd best paper).


Two major obstacles to the use of consumer camcorders in computer vision applications are the lack of synchronization hardware, and the use of a "rolling" shutter, which introduces a temporal shear in the video volume. We present two simple approaches for solving both the rolling shutter shear and the synchronization problem at the same time. The first approach is based on strobe illumination, while the second employs a subframe warp along optical flow vectors. In our experiments we have used the proposed methods to effectively remove temporal shear, and synchronize up to 16 consumer-grade camcorders in multiple geometric configurations.
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author = {Derek Bradley and Bradley Atcheson and Ivo Ihrke and Wolfgang Heidrich},
title = {Synchronization and Rolling Shutter Compensation for Consumer Video Camera Arrays},
journal = {International Workshop on Projector-Camera Systems (PROCAMS 2009)},
year = {2009},
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