Estimation of absolute depth from polarization measurements
A head mounted display comprises an eye tracking system configured to enable eye tracking using polarization. The eye tracking system includes one or more illumination sources and an optical detector comprising polarization sensitive pixels. The one or more illumination sources are configured to illuminate a user's eye and generate reflections directed towards the optical detector. The eye tracking system determines, for each polarization sensitive pixel in a subset of the polarization sensitive pixels, one or more estimation parameters. The eye tracking system determines, for the subset of the polarization sensitive pixels, depth information for one or more glints associated with one or more surfaces of the eye, based in part on the polarization of the reflections and the one or more estimation parameters. The determined depth information is used to update a model of the eye. The eye tracking system determines eye tracking information based on the updated model.
1. An eye tracking system comprising:
a polarization sensitive detector configured to:
capture one or more images of an eye, and
determine polarization information for the one or more images; and
a controller configured to:
determine depth information for at least one glint associated with at least one surface of the eye using the polarization information and at least one estimation parameter associated with the polarization sensitive detector, and
determine a gaze direction for the eye using the depth information.
2. The eye tracking system of claim 1 , wherein the controller is further configured to:
generate a model of the eye by fitting at least one component of the model to the at least one surface of the eye using the depth information; and
determine the gaze direction for the eye based on the generated model of the eye.
3. The eye tracking system of claim 1 , wherein the polarization sensitive detector comprises an array of polarization sensitive elements.
4. The eye tracking system of claim 3 , wherein at least one polarization sensitive element in the array comprises a plurality of native pixels.
5. The eye tracking system of claim 4 , at least one of the native pixels comprises a polarization filter.
6. The eye tracking system of claim 1 , wherein the controller is further configured to:
determine a plurality of surface normals using the polarization information;
determine a three-dimensional (3D) shape of the eye using the surface normals; and
determine the gaze direction for the eye using the determined 3D shape of the eye.
7. The eye tracking system of claim 1 , wherein the polarization sensitive detector is configured to detect intensities of light reflected from the at least one surface of the eye and captured by the polarization sensitive detector at multiple polarization angles.
8. The eye tracking system of claim 7 , wherein the controller is further configured to:
determine a degree of polarization of the reflected light using the detected intensities;
determine a zenith angle associated with the reflected light using the determined degree of polarization; and
determine the depth information for the at least one glint based on the at least one estimation parameter and the zenith angle.
9. The eye tracking system of claim 1 , wherein the at least one estimation parameter comprises: at least one displacement between at least one illumination source illuminating the at least one surface of the eye and at least one polarization sensitive element of the polarization sensitive detector, and at least one angle between at least one ray of light reflected from the at least one surface of the eye and at least one axis of the at least one polarization sensitive element capturing the at least one ray of reflected light.
10. The eye tracking system of claim 9 , wherein:
the polarization sensitive detector is configured to detect intensities of light reflected from the at least one surface of the eye and captured by the polarization sensitive detector at multiple polarization angles; and
the controller is further configured to:
determine a degree of polarization of the reflected light using the detected intensities,
determine a zenith angle associated with the reflected light using the degree of polarization, and
determine the depth information for the at least one glint based on the at least one displacement, the at least one angle and the zenith angle.
11. The eye tracking system of claim 1 , wherein the controller is further configured to:
extract one or more model parameter values from the depth information;
generate a model of the eye using the one or more extracted model parameters values; and
determine the gaze direction for the eye based on the generated model of the eye.
12. The eye tracking system of claim 1 , wherein the polarization sensitive detector comprises a dynamic polarizer permeable to light of a defined set of polarization states.
13. The eye tracking system of claim 1 , wherein the eye tracking system is part of a headset.
14. A method comprising:
capturing, at a polarization sensitive detector, one or more images of an eye;
determining polarization information for the one or more images;
determining depth information for at least one glint associated with at least one surface of the eye using the polarization information and at least one estimation parameter associated with the polarization sensitive detector; and
determining a gaze direction for the eye using the depth information.
15. The method of claim 14 , further comprising:
generating a model of the eye by fitting at least one component of the model to the at least one surface of the eye using the depth information; and
determining the gaze direction for the eye based on the generated model of the eye.
16. The method of claim 14 , further comprising:
determining a plurality of surface normals using the polarization information;
determining a three-dimensional (3D) shape of the eye using the surface normals; and
determining the gaze direction for the eye using the determined 3D shape of the eye.
17. The method of claim 14 , further comprising:
detecting intensities of light reflected from the at least one surface of the eye and captured by the polarization sensitive detector at multiple polarization angles;
determining a degree of polarization of the reflected light using the detected intensities;
determining a zenith angle associated with the reflected light using the determined degree of polarization; and
determining the depth information for the at least one glint based on the at least one estimation parameter and the zenith angle.
18. The method of claim 14 , wherein the at least one estimation parameter comprises: at least one displacement between at least one illumination source illuminating the at least one surface of the eye and at least one polarization sensitive element of the polarization sensitive detector, and at least one angle between at least one ray of light reflected from the at least one surface of the eye and at least one axis of the at least one polarization sensitive element capturing the at least one ray of reflected light.
19. The method of claim 18 , further comprising:
detecting intensities of light reflected from the at least one surface of the eye and captured by the polarization sensitive detector at multiple polarization angles;
determining a degree of polarization of the reflected light using the detected intensities;
determining a zenith angle associated with the reflected light using the determined degree of polarization; and
determining the depth information for the at least one glint based on the at least one displacement, the at least one angle and the zenith angle.
20. The method of claim 14 , further comprising:
extracting one or more model parameter values from the depth information;
generating a model of the eye using the one or more extracted model parameters values; and
determining the gaze direction for the eye based on the updated model of the eye.