Robust pupil center detection using a curvature algorithm.

Determining the pupil center is fundamental for calculating eye orientation in video-based systems. Existing techniques are error prone and not robust because eyelids, eyelashes, corneal reflections or shadows in many instances occlude the pupil. We have developed a new algorithm which utilizes curvature characteristics of the pupil boundary to eliminate these artifacts. Pupil center is computed based solely on points related to the pupil boundary. For each boundary point, a curvature value is computed. Occlusion of the boundary induces characteristic peaks in the curvature function. Curvature values for normal pupil sizes were determined and a threshold was found which together with heuristics discriminated normal from abnormal curvature. Remaining boundary points were fit with an ellipse using a least squares error criterion. The center of the ellipse is an estimate of the pupil center. This technique is robust and accurately estimates pupil center with less than 40% of the pupil boundary points visible.

[1]  W. Gander,et al.  Least-squares fitting of circles and ellipses , 1994 .

[2]  L. Young,et al.  Survey of eye movement recording methods , 1975 .

[3]  I S Curthoys,et al.  VTM--an image-processing system for measuring ocular torsion. , 1991, Computer methods and programs in biomedicine.

[4]  Mehdi Hatamian,et al.  Design Considerations for a Real-Time Ocular Counterroll Instrument , 1983, IEEE Transactions on Biomedical Engineering.

[5]  T Viéville,et al.  Ocular Counter-rolling during Active Head Tilting in Humans. , 1987, Acta oto-laryngologica.

[6]  B. Cohen,et al.  Coding of information about rapid eye movements in the pontine reticular formation of alert monkeys , 1976, Brain Research.

[7]  B Cohen,et al.  Semicircular canal contributions to the three-dimensional vestibuloocular reflex: a model-based approach. , 1995, Journal of neurophysiology.

[8]  James H. McKay,et al.  Analytic geometry and calculus , 1961 .

[9]  Dana H. Ballard,et al.  Computer Vision , 1982 .

[10]  Steven T. Moore,et al.  A geometric basis for measurement of three-dimensional eye position using image processing , 1996, Vision Research.

[11]  J.E. Bos,et al.  Ocular torsion quantification with video images , 1994, IEEE Transactions on Biomedical Engineering.

[12]  H. F. Li,et al.  Real-time on-line pattern recognition of eye position and movement , 1985 .

[13]  N. Shimizu.  [Neurology of eye movements]. , 2000, Rinsho shinkeigaku = Clinical neurology.

[14]  C. Schnabolk,et al.  Modeling three-dimensional velocity-to-position transformation in oculomotor control. , 1994, Journal of neurophysiology.

[15]  F. A. Seiler,et al.  Numerical Recipes in C: The Art of Scientific Computing , 1989 .

[16]  J B Mulligan,et al.  Image processing for improved eye-tracking accuracy , 1997, Behavior research methods, instruments, & computers : a journal of the Psychonomic Society, Inc.

[17]  Kwangjae Sung,et al.  Analysis Of Two Video Eye Tracking Algorithms , 1991, Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society Volume 13: 1991.

[18]  J. A. Parker,et al.  Measurement of Torsion from Multitemporal Images of the Eye Using Digital Signal Processing Techniques , 1985, IEEE Transactions on Biomedical Engineering.

[19]  J Merchant,et al.  Remote measurement of eye direction allowing subject motion over one cubic foot of space. , 1974, IEEE transactions on bio-medical engineering.

[20]  T. Haslwanter,et al.  A theoretical analysis of three-dimensional eye position measurement using polar cross-correlation , 1995, IEEE Transactions on Biomedical Engineering.

[21]  William H. Press,et al.  The Art of Scientific Computing Second Edition , 1998 .

[22]  D. Robinson.  Eye movements evoked by collicular stimulation in the alert monkey. , 1972, Vision research.

[23]  D Tweed,et al.  Implications of rotational kinematics for the oculomotor system in three dimensions. , 1987, Journal of neurophysiology.

[24]  E. Groen,et al.  Determination of ocular torsion by means of automatic pattern recognition , 1996, IEEE Transactions on Biomedical Engineering.

[25]  T. Viéville,et al.  Ocular Counter-rolling during Active Head Tilting in Humans. , 1987, Acta oto-laryngologica.