Timer-based eye-tracking
Aspects of the present disclosure describe systems, methods, and structures that provide eye-tracking by 1) steering a beam of light through the effect of a microelectromechanical system (MEMS) onto a surface of the eye and 2) detecting light reflected from features of the eye including corneal surface, pupil, iris—among others. Positional/geometric/feature/structural information pertaining to the eye is determined from timing information associated with the reflected light.
1. A timer-based eye-tracking method comprising:
steering a first beam of light in a two-dimensional pattern over a first region of an eye that includes a pupil, an iris, a cornea, and a lens;
detecting light reflected from the first region;
producing a first electrical signal that includes electrical pulses in response to the detection;
comparing the electrical pulses to a first threshold to determine the characteristic;
determining a feature of the eye by a characteristic of the electrical pulses so produced, wherein the characteristic is selected from the group consisting of pulse width, leading edge, and last edge;
identifying a first plurality of times when the magnitude of the electrical pulses crosses the first threshold; and
establishing a first contour of the feature based on the first plurality of times.
2. The method of claim 1 further comprising determining the position of the first beam of light in at least one dimension within the first region based on a first time at which the electrical pulse magnitude is equal to the first threshold.
3. The method of claim 1 further comprising:
determining a first value of the first electrical signal that corresponds to diffuse reflection from the iris;
determining a second value of the first electrical signal that corresponds to the pupil;
establishing the first threshold such that it is between the first and second values;
performing an ellipse fitting technique based on a plurality of times at which the first electrical signal crosses the first threshold; and
estimating a pupil size based on the fitted ellipse.
4. The method of claim 3 further comprising:
detecting the light reflected from the first region at multiple detectors that provide a plurality of second electrical signals; and
summing the plurality of second electrical signals to realize the first electrical signal.
5. The method of claim 3 further comprising applying at least one correction factor to the fitted ellipse to compensate for at least one of (1) a refractive index of the cornea, (2) the refractive index of the lens, and (3) a gaze direction of the eye.
6. The method of claim 1 wherein the feature is the pupil.
7. The method of claim 1 further comprising:
identifying a second plurality of times when the magnitude of the electrical pulses crosses a second threshold; and
establishing a second contour of the feature based on the second plurality of times.
8. The method of claim 1 further comprising determining a gaze direction of the eye based on the detected reflected light.
9. The method of claim 1 wherein the first beam of light is steered in the two-dimensional pattern based on at least one drive signal that includes a direct current (DC) component, and wherein the method further includes adjusting the DC component to induce a shift in the two-dimensional pattern.
10. The method of claim 9 wherein the shift induces panning of the first beam of light such that it is steered in the two-dimensional pattern over a second region of the eye.
11. The method of claim 1 wherein the light reflected from the first region is detected by multiple detectors that provide a plurality of electrical signals that includes the electrical pulses, the plurality of electrical signals including the first electrical signal.
12. The method of claim 11 further comprising:
making a first comparison of the electrical signals of the plurality thereof; and
determining the feature of the eye based further on the first comparison.
13. The method of claim 11 further comprising:
establishing a first threshold for the first electrical signal;
establishing a second threshold for a second electrical signal of the plurality thereof; and
comparing the electrical pulses to at least one of the first and second thresholds to determine the characteristic.
14. The method of claim 1 wherein the first beam of light is modulated.
15. The method of claim 1 further comprising steering a second beam of light in a two-dimensional pattern over the first region of the eye.
16. A timer-based eye-tracking system comprising:
a first scanner for steering a first beam of light in a two-dimensional pattern over a first region of the eye;
a detector module for detecting light reflected from the first region and producing a first electrical signal that includes electrical pulses in response to the detection; and
a processor configured to:
determine a feature of the eye based on a characteristic of the electrical pulses so produced, wherein the characteristic is selected from the group consisting of pulse width, leading edge, and last edge;
compare the electrical pulses to a first threshold to determine the characteristic; and
determine a first contour of the feature based on a first plurality of times at which a magnitude of the electrical pulses crosses the first threshold.
17. The system of claim 16 wherein the detector module includes a plurality of detectors for detecting light reflected from the first region and producing a plurality of electrical signals that collectively define the first electrical signal.
18. The system of claim 16 further including a second scanner for steering a second beam of light in a two-dimensional pattern over the first region.
19. The system of claim 16 wherein the processor is further configured to establish a second contour of the feature based on a second plurality of times when the magnitude of the electrical pulses crosses a second threshold.
20. The system of claim 16 wherein the processor is further configured to determine a gaze direction of the eye based on the detected reflected light.
21. The system of claim 16 wherein the first scanner steers the first beam of light in response to a first drive signal, and wherein the first drive signal includes a direct current (DC) component that is controllable to induce a shift in the first two-dimensional pattern.
22. The system of claim 21 wherein the shift pans the first light signal such that it is steered in the two-dimensional pattern over a second region of the eye.