Variable Focal Plane Displays for Accurate Depth Perception
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Solution Overview
Problem
Conventional 3-D displays, particularly head-mounted stereoscopic displays, suffer from visual artifacts such as distortions, visual fatigue, and inaccurate depth perception due to the decoupling of accommodation and convergence cues, and lack the capability to render correct focus cues efficiently, limiting their acceptance for demanding applications.
Innovation Solution
The development of stereoscopic displays with addressable focal planes that use a liquid lens or active-optical elements to modulate the focal distance of light patterns in a time-sequential manner, providing accurate focus cues with reduced computational power, enabling more natural depth perceptions and improved usability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional stereoscopic displays present images on a fixed image plane, then device complexity is reduced, but depth perception accuracy deteriorates due to decoupling of accommodation and convergence cues
Solution Approach 1:
The patent implements a variable focal plane display system where the image plane can dynamically change its position along the optical axis. This allows the display to present stereoscopic images at different focal distances, enabling the accommodation cue to match the convergence cue for objects at different depths. The dynamic adjustment of the image plane position resolves the contradiction by making the display structure adaptable rather than fixed, thereby improving depth perception accuracy without excessive complexity increase.
Solution Approach 2:
The display system segments the viewing space into multiple depth planes, with each plane capable of being independently focused. By dividing the continuous depth space into discrete focal planes that can be selectively activated, the system provides accurate accommodation cues for objects at different depths while maintaining a manageable device structure. This segmentation approach allows the display to present multiple focal distances without requiring a completely complex continuous adjustment mechanism.
2Ease of operation
If conventional displays force eyes to converge at different distances on a fixed image plane, then ease of operation is improved, but visual fatigue increases due to erroneous focus cues
Solution Approach 1:
The variable focal plane display dynamically adjusts the image plane position to match the convergence distance of the user's eyes. This dynamic coupling of accommodation and convergence cues eliminates the erroneous focus information that causes visual fatigue in conventional displays. The system maintains ease of operation by automatically tracking and adapting to the user's viewing conditions without requiring manual intervention, thereby resolving the contradiction between usability and visual comfort.
Solution Approach 2:
The display system incorporates feedback mechanisms that monitor the user's convergence behavior and adjust the focal plane position accordingly. This feedback loop ensures that the accommodation cue provided by the display matches the convergence cue, preventing the decoupling that leads to visual fatigue. The feedback-driven adjustment maintains natural viewing conditions while preserving ease of operation.
3Measurement precision
If volumetric displays render millions of voxels within a physical volume, then depth perception accuracy is improved, but productivity deteriorates due to low rendering efficiency
Solution Approach 1:
The patent extracts the essential depth perception capability from complex volumetric rendering by using a variable focal plane approach with 2-D micro-displays. Instead of rendering millions of voxels to create true 3-D volume, the system extracts depth information by presenting 2-D images at different focal planes that the human visual system interprets as 3-D. This extraction approach maintains depth perception accuracy while dramatically improving rendering efficiency, as it avoids the computational burden of full volumetric rendering.
Solution Approach 2:
Rather than creating true 3-D volumetric images through complex voxel rendering, the patent inverts the approach by using 2-D displays at different focal distances to simulate 3-D depth perception. This inversion leverages the human visual system's ability to interpret depth from focal plane variations, achieving accurate depth perception without the computational expense of volumetric rendering. The method trades the complexity of volume rendering for the simplicity of focused 2-D image presentation.
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 solution provides improved depth perceptions and reduced visual fatigue by accurately rendering focus cues with less computational power, making the displays more suitable for demanding applications and daily usage.
Implementation Method 1
A liquid lens, being refractive, allows the display to be compact and practical, including for head-mounted use, without compromising the required accommodation range
Implementation Method 2
The active-optical element has variable optical power and is addressable to change its optical power to produce a corresponding change in perceived distance
Data Source
AI summary
A display placed in an optical pathway extending from an entrance pupil of a person's eye to a real-world scene beyond the eye. The display includes at least one 2-D added-image source that is addressable to produce a light pattern corresponding to a virtual object. The source is situated to direct the light pattern toward the person's eye to superimpose the virtual object on an image of the real-world scene as perceived by the eye via the optical pathway. An active-optical element is situated between the eye and the added-image source at a location that is optically conjugate to the entrance pupil and at which the active-optical element forms an intermediate image of the light pattern from the added-image source. The active-optical element has variable optical power and is addressable to change its optical power to produce a corresponding change in perceived distance at which the intermediate image is formed, as an added image to the real-world scene, relative to the eye.