Hybrid cornea and pupil tracking
A hybrid cornea and pupil eye-tracking technique includes receiving iris-backscattered light from an eye and determining a pupil-position of the eye based on the iris-backscattered light. Cornea-reflected light is received from the eye and an eye-tracking position of the eye is determined based on the cornea-reflected light and the pupil-position.
1. A method comprising:
illuminating an eye with non-visible light at a first intensity;
capturing a first eye-tracking image that includes a pupil of the eye while the eye is illuminated by the first intensity of the non-visible light;
illuminating the eye with the non-visible light at a second intensity that is less than the first intensity of the non-visible light;
capturing a second eye-tracking image that includes cornea glints while the eye is illuminated at the second intensity of the non-visible light that is less than the first intensity;
determining a cornea-position of the eye based on the second eye-tracking image;
determining a gaze direction of the eye based on the cornea-position and the first eye-tracking image that includes the pupil;
detecting a blink event of the eye;
increasing the non-visible light to the first intensity from the second intensity in response to detecting the blink event of the eye;
capturing a subsequent eye-tracking image of the pupil while the eye is illuminated by the first intensity of the non-visible light; and
determining a subsequent gaze direction of the eye based on the subsequent eye-tracking image, wherein the subsequent gaze direction is determined subsequent to determining the cornea-position of the eye.
2. The method of claim 1 , wherein the second eye-tracking image lacks sufficient contrast to determine a pupil-position of the eye.
3. The method of claim 1 , wherein determining the gaze direction of the eye includes deriving a pupil-center coordinate from the first eye-tracking image.
4. The method of claim 1 , wherein the non-visible light is near-infrared light.
5. The method of claim 1 , wherein illuminating the eye with non-visible light includes illuminating the eye with in-field illuminators of a near-eye optical element, and wherein the in-field illuminators are disposed in a field of view (FOV) of the eye.
6. A near-eye optical system comprising:
an infrared light source configured to illuminate an eye with infrared light;
a camera configured to capture images of the eye, wherein the camera is configured to receive a wavelength that matches the infrared light emitted by the infrared light source and reject other light, and wherein the near-eye optical system is configured to:
drive the infrared light source to illuminate the eye with the infrared light at a first intensity;
capture, with the camera, a first eye-tracking image that includes a pupil of the eye while the eye is illuminated by the first intensity of infrared light;
drive the infrared light source to illuminate the eye with the infrared light at a second intensity that is less than the first intensity;
capture cornea glints while the eye is illuminated at the second intensity that is less than the first intensity;
determine a cornea-position of the eye based on the captured cornea glints;
determine a gaze direction of the eye based on the cornea-position and the first eye-tracking image that includes the pupil;
detecting a blink event of the eye;
increasing the infrared light to the first intensity from the second intensity in response to detecting the blink event of the eye;
capturing a subsequent eye-tracking image of the pupil while the eye is illuminated by the first intensity of the infrared light; and
determining a subsequent gaze direction of the eye based on the subsequent eye-tracking image, wherein the subsequent gaze direction is determined subsequent to determining the cornea-position of the eye.
7. The near-eye optical system of claim 6 , wherein determining the gaze direction of the eye includes deriving a pupil-center coordinate from the first eye-tracking image.
8. The near-eye optical system of claim 6 , wherein the infrared light source is an in-field illuminator of a near-eye optical element, and wherein the in-field illuminator is disposed in a field of view (FOV) of the eye.
9. The near-eye optical system of claim 6 , wherein the first intensity is more than ten times greater than the second intensity.
10. The near-eye optical system of claim 6 , wherein the infrared light is near-infrared light.
11. The near-eye optical system of claim 6 further comprising angle-sensitive photodiodes for capturing the cornea glints.
12. The method of claim 1 , wherein the gaze direction of the eye is further based on a cornea-center of the cornea-position and a vector through the cornea-center and a pupil-center of the pupil.
13. The near-eye optical system of claim 6 , wherein the gaze direction of the eye is further based on a cornea-center of the cornea-position and a vector through the cornea-center and a pupil-center of the pupil.