Sign Language Fingerspelling Classification from Depth and Color Images using a Deep Belief Network

Automatic sign language recognition is an open problem that has received a lot of attention recently, not only because of its usefulness to signers, but also due to the numerous applications a sign classifier can have. In this article, we present a new feature extraction technique for hand pose recognition using depth and intensity images captured from a Microsoft Kinect sensor. We applied our technique to American Sign Language fingerspelling classification using a Deep Belief Network, for which our feature extraction technique is tailored. We evaluated our results on a multi-user data set with two scenarios: one with all known users and one with an unseen user. We achieved 99% recall and precision on the first, and 77% recall and 79% precision on the second. Our method is also capable of real-time sign classification and is adaptive to any environment or lightning intensity.Comment: Published in 2014 Canadian Conference on Computer and Robot Visio

The Implications of Gunn-Peterson Troughs in the HeII Lyman-alpha Forest

Many experts believe that the z ~ 3 HeII Ly-alpha forest will suffer from the same saturation issues as the z ~ 6 HI Ly-alpha forest and, therefore, will not be a sensitive probe of HeII reionization. However, there are several factors that make HeII Ly-alpha absorption more sensitive than HI Ly-alpha. We show that observations of HeII Ly-alpha and Ly-beta Gunn-Peterson troughs can provide a relatively model-independent constraint on the volume-averaged HeII fraction of x_HeII >~ 0.1. This bound derives from first using the most underdense regions in the HeII forest to constrain the local HeII fraction and, then, assuming photoionization equilibrium with the maximum allowed photoionization rate to calculate the ionization state of nearby gas. It is possible to evade this constraint by a factor of ~2, but only if the HeII were reionized recently. We argue that HeII Ly-alpha Gunn-Peterson troughs observed in the spectra of Q0302-003 and HE2347-4342 signify the presence of >~ 10 comoving Mpc patches in which x_HeII > 0.03. This is a factor of 20 improvement over previous constraints from these spectra and 100 times stronger than the tightest constraint on the HI volume-filling fraction from the z>6 HI Lyman forest.Comment: 5 pages, 4 figures, includes some supplementary text not in ApJ Letter versio