Eye Center of Rotation Determination in Head-Mounted Displays
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Solution Overview
Problem
Current virtual reality, augmented reality, and mixed reality technologies face challenges in providing a comfortable and natural-feeling presentation of virtual image elements amidst real-world imagery due to complexities in human visual perception, particularly in accurately determining depth planes and user eye dynamics.
Innovation Solution
A display system configured with a head-mounted frame, eye tracking cameras, and processing electronics that project light into the user's eye to adjust divergence and collimation, determining the center of rotation, optical axis, and vergence distance based on eye images, allowing for dynamic rendering of virtual content that appears to originate from different depths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If eye tracking cameras are used to determine eye parameters, then depth perception accuracy is improved, but device complexity increases
Solution Approach 1:
The patent introduces a render camera as an intermediary virtual camera positioned at the user's eye center of rotation. This render camera captures virtual images that are then displayed to the user, effectively mediating between the computational depth calculation and the visual presentation. The render camera's virtual position at the eye center enables accurate depth perception without requiring complex physical eye-tracking hardware adjustments.
Solution Approach 2:
The system creates a virtual copy of the user's eye parameters (center of rotation, optical axis, interpupillary distance) and uses this copy to position the render camera. By copying these anatomical parameters into the virtual rendering space, the system can accurately simulate depth perception without physically modifying the user's eyes or requiring complex adaptive optics.
2Ease of manufacture
If virtual images are displayed at different depths, then realism is improved, but eye strain increases
Solution Approach 1:
The system dynamically adjusts the render camera's position and the virtual images' depth parameters in real-time based on the user's eye movements and gaze direction. As the user's eyes move, the render camera repositions to track these movements, maintaining proper focus and accommodation cues. This dynamic adaptation prevents eye strain by keeping the visual system's focus and accommodation mechanisms aligned with the displayed content.
Solution Approach 2:
The system incorporates feedback from eye tracking cameras that continuously monitor the user's eye position, pupil dilation, and gaze direction. This feedback is used to adjust the render camera's position and the virtual images' depth parameters, creating a closed-loop system that adapts to user needs. The feedback mechanism ensures that depth information is presented in a way that naturally accommodates the user's visual system, reducing strain.
3Measurement precision
If eye center of rotation is dynamically determined, then depth plane selection is improved, but processing requirements increase
Solution Approach 1:
The system performs preliminary estimation of eye parameters (center of rotation, optical axis) using standard eye tracking algorithms and then refines these estimates by analyzing corneal curvature and glint positions. By breaking down the complex calculation into preliminary and refinement steps, the system achieves high accuracy without requiring all calculations to be performed simultaneously at maximum complexity.
Solution Approach 2:
The system changes the parameters used for depth calculation based on the detected eye state and viewing conditions. When the user's eyes are stationary, simpler parameters are used; when eyes are moving or focusing on specific depths, more complex parameters including corneal curvature and glint analysis are activated. This parameter adaptation allows the system to maintain high accuracy while reducing processing requirements during simpler viewing states.
Data Source
AI summary
A display system can include a head-mounted display configured to project light to an eye of a user to display virtual image content at different amounts of divergence and collimation. The display system can include an inward-facing imaging system that images the user's eye and processing electronics that are in communication with the inward-facing imaging system and that are configured to obtain an estimate of a center of rotation of the user's eye. The display system may render virtual image content with a render camera positioned at or relative to the center of rotation of the eye.