New methods for an eye-tracker based on multiple corneal reflections
Clara Mestre, Josselin Gautier, Jaume Pujol
Video oculography based on interpolation methods are widely used for gaze tracking purposes. Here we define new methods for a high resolution darkpupil eye-tracker with multiple IR LED light sources to improve its accuracy and robustness against head movements and eyelid occlusion.
- The Eye and Vision Analyzer (EVA) (DAVALOR, Spain) is a new 3D virtual reality system to assess human visual function. It embeds a dark-pupil based eye-tracker with twelve IR LEDs.
- Starburst algorithm is a robust algorithm commonly used by the eye tracking community to track the eye position from infrared eye images.
- Normalization of the pupil-glint (PG) vector by the interglint distance has been shown to improve the accuracy of the eye-tracker, especially when head movement is allowed. Can we improve it further?
- Is the use of twelve light sources justified by an improved eye-tracker’s performance?
- Eye images of seven subjects (age 20-29 years) were taken by means of current EVA’s eye-tracker cameras (resolution: 640 x 480 pixels per eye, frame rate: 30 Hz) during calibration and validation procedures in which the subjects were asked to fixate a cross which appeared randomly on a 3 x 3 grid.
- All images have been processed offline with Starburst algorithm, which has been extended to fit EVA’s eye-tracker requirements and characteristics.
- The point of regard (PoR) has been computed from the position of the pupil and glints with a second order interpolation equation.
- The normalization of the PG vectors improves significantly the eye-tracker’s accuracy in all five configurations. The improvement is greater in those configurations in which the real positions of the glints are considered, i.e. with 2, 4 and 6 glints.
- The accuracy tends to increase with the number of glints (although not significantly here, for n=7 subjects), especially when normalization is not applied. However, the best results in terms of pupil and glints stability are shown with 4 and 6 glints.
- These trends need to be confirmed with a larger eye images database in order to determine which is the best light sources configuration.
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