Polarization-Sensitive Eye Tracking for HMD Depth Estimation
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Solution Overview
Problem
Conventional eye tracking systems for head-mounted display (HMD) systems face limitations in accuracy due to variations in human eye geometry and sub-surface scattering, which affect the estimation of absolute depth and optical axis tracking.
Innovation Solution
An eye tracking system that utilizes polarization-sensitive cameras and illumination sources to capture and analyze polarized light reflections from the eye, determining depth information and eye tracking parameters to accurately model the eye's geometry and orientation, enabling precise gaze direction and vergence angle estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional tracking systems use patterned illumination and standard imaging cameras to detect glints, then the system structure is simple, but the measurement precision of eye position and optical axis is insufficient
Solution Approach 1:
The patent replaces standard imaging cameras with polarization-sensitive cameras that can measure the polarization state of reflected light. This substitution enables precise determination of surface normals and eye geometry by analyzing polarization angles, significantly improving measurement precision for eye position and optical axis tracking while maintaining a relatively simple system structure.
Solution Approach 2:
The patent utilizes the polarization state of light as an additional measurement parameter beyond intensity. By measuring the polarization angle of glints reflected from the eye, the system can accurately determine surface normals and corneal geometry, resolving the contradiction between simple structure and high precision through the introduction of polarization parameter measurement.
2Measurement precision
If conventional systems assume spherical eyeball geometry, then the device complexity is reduced, but the measurement precision deteriorates due to individual eye variations
Solution Approach 1:
The patent applies local quality by measuring polarization angles at multiple specific locations (multiple glints) across the corneal surface rather than assuming uniform spherical geometry. Each measurement point provides local surface normal information, which collectively reconstructs the actual non-spherical eye geometry with high precision, accounting for individual variations without requiring complex prior models.
Solution Approach 2:
The system uses feedback by iteratively refining the eye model based on polarization measurements from multiple glints. The measured polarization angles provide feedback on the actual corneal surface normals, allowing the system to adjust and optimize the eye geometry model to match the individual user's actual eye shape, improving precision while managing complexity through iterative optimization.
3Measurement precision
If standard imaging cameras are used to capture eye reflections, then the device complexity is low, but the measurement precision of surface normals and depth information is insufficient
Solution Approach 1:
The patent substitutes standard imaging cameras with polarization-sensitive cameras capable of measuring the polarization state of light. This enables precise determination of surface normals by analyzing the polarization angle of reflected glints, as the polarization state directly encodes surface orientation information, achieving high measurement precision for depth and surface geometry.
Solution Approach 2:
The system changes the measured parameter from only light intensity to include polarization angle. This additional parameter provides direct information about surface normals through the relationship between polarization angle and incidence angle, enabling accurate depth estimation and surface geometry reconstruction without requiring complex imaging systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides enhanced accuracy in tracking eye movements and depth estimation, improving the capabilities of HMD systems for applications like foveated rendering and vergence-accommodation alignment by accounting for individual eye variations and scattering effects.
Implementation Method 1
An eye tracking system is disclosed which tracks a user's eye based in part on polarization of light reflected from the user's eye
Implementation Method 2
The optical detector and the one or more illumination sources are positioned relative to each other such that the optical detector is able to capture light emitted by the one or more illumination sources and reflected from one or more surfaces of the user's eye
Data Source
AI summary
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.