Eye tracking in the wild

An active contour tracker is presented which can be used for gaze-based interaction with off-the-shelf components. The underlying contour model is based on image statistics and avoids explicit feature detection. The tracker combines particle filtering with the EM algorithm. The method exhibits robustness to light changes and camera defocusing; consequently, the model is well suited for use in systems using off-the-shelf hardware, but may equally well be used in controlled environments, such as in IR-based settings. The method is even capable of handling sudden changes between IR and non-IR light conditions, without changing parameters. For the purpose of determining where the user is looking, calibration is usually needed. The number of calibration points used in different methods varies from a few to several thousands, depending on the prior knowledge used on the setup and equipment. We examine basic properties of gaze determination when the geometry of the camera, screen, and user is unknown. In particular we present a lower bound on the number of calibration points needed for gaze determination on planar objects, and we examine degenerate configurations. Based on this lower bound we apply a simple calibration procedure, to facilitate gaze estimation. (C) 2004 Elsevier Inc. All rights reserved.