Pupil Detection and Tracking Using Multiple Light Sources

We present a fast, robust, and low cost pupil detection technique that uses two infra red (IR) time multiplexed light sources, composed of two rings of 8 LED's each, synchronized with the camera frame rate. One light source is placed very close to the camera's optical axis, and the second source is placed off-axis. The pupil appears bright in the camera image during on-axis illumination (similar to the red eye effect from flash photography),and dark when illumination is off-axis. The off-axis light source is calibrated to provide roughly-equivalent whole-scene illumination. Pupil detection follows from thresholding the difference of the dark from the bright pupil images. To reduce artifacts caused mostly by head motion, a larger temporal support is used. This method can be
applied to detect and track several pupils (or several people).
Experimental results from a real-time implementation of the system show that this technique is very robust, and able to detect pupils using wide field of view low cost cameras under different illumination conditions, even for people with glasses, and up to 5m from the camera.