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New methods for an eye-tracker based on multiple corneal reflections

Compartir 08/09/2016 Publicaciones Científicas

Clara Mestre, Josselin Gautier, Jaume Pujol

Purpose

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.

Introduction

  • 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?

Methods

  • 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.

Conclusions

  • 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.
new-methods-for-an-eye-tracker-based-on-multiple-corneal-reflections-mestre.pdf

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