Depth cue: Difference between revisions
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{{see also|Terms|Technical Terms}} | {{see also|Terms|Technical Terms}} | ||
[[Depth cue]] is any of a variety of perceptual signals that allow the [[human visual system]] to infer the distance or depth of objects in a scene, enabling the brain to transform two-dimensional retinal images into a perception of three-dimensional space. <ref name="HowardRogers2012">Howard, I. P., & Rogers, B. J. (2012). *Perceiving in Depth, Volume 1: Basic Mechanisms*. Oxford University Press.</ref> These cues are crucial for navigating the three-dimensional world and are fundamental to creating convincing, immersive, and comfortable experiences in [[Virtual Reality]] (VR) and [[Augmented Reality]] (AR), where reproducing accurate depth perception presents significant technical challenges. <ref name="HowardRogers1995">Howard, Ian P., and Brian J. Rogers. (1995). *Binocular vision and stereopsis*. Oxford University Press.</ref> The brain automatically fuses multiple available depth cues to build a robust model of the spatial layout of the environment. <ref name="HITLCues1">(2014-06-20) Visual Depth Cues - Human Interface Technology Laboratory. Retrieved April 25, 2025, from https://www.hitl.washington.edu/projects/ | [[Depth cue]] is any of a variety of perceptual signals that allow the [[human visual system]] to infer the distance or depth of objects in a scene, enabling the brain to transform two-dimensional retinal images into a perception of three-dimensional space. <ref name="HowardRogers2012">Howard, I. P., & Rogers, B. J. (2012). *Perceiving in Depth, Volume 1: Basic Mechanisms*. Oxford University Press.</ref> These cues are crucial for navigating the three-dimensional world and are fundamental to creating convincing, immersive, and comfortable experiences in [[Virtual Reality]] (VR) and [[Augmented Reality]] (AR), where reproducing accurate depth perception presents significant technical challenges. <ref name="HowardRogers1995">Howard, Ian P., and Brian J. Rogers. (1995). *Binocular vision and stereopsis*. Oxford University Press.</ref> The brain automatically fuses multiple available depth cues to build a robust model of the spatial layout of the environment. <ref name="HITLCues1">(2014-06-20) Visual Depth Cues - Human Interface Technology Laboratory. Retrieved April 25, 2025, from https://www.hitl.washington.edu/projects/knowledge-base/virtual-worlds/EVE/III.A.1.b.VisualDepthCues.html</ref> | ||
== Classification of Depth Cues == | == Classification of Depth Cues == | ||
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====The [[Vergence-Accommodation Conflict]] (VAC)==== | ====The [[Vergence-Accommodation Conflict]] (VAC)==== | ||
A major limitation in most current VR/AR displays is the mismatch between vergence and accommodation cues. Most headsets use [[fixed-focus display]]s, meaning the optics present the virtual image at a fixed focal distance (often 1.5-2 meters or optical infinity), regardless of the simulated distance of the virtual object. <ref name="ARInsiderVAC">(2024-01-29) Understanding Vergence-Accommodation Conflict in AR/VR Headsets - AR Insider. Retrieved April 25, 2025, from https://arinsider.co/ | A major limitation in most current VR/AR displays is the mismatch between vergence and accommodation cues. Most headsets use [[fixed-focus display]]s, meaning the optics present the virtual image at a fixed focal distance (often 1.5-2 meters or optical infinity), regardless of the simulated distance of the virtual object. <ref name="ARInsiderVAC">(2024-01-29) Understanding Vergence-Accommodation Conflict in AR/VR Headsets - AR Insider. Retrieved April 25, 2025, from https://arinsider.co/2024/01/29/understanding-vergence-accommodation-conflict-in-ar-vr-headsets/</ref> <ref name="WikiVAC">Vergence-accommodation conflict - Wikipedia. Retrieved April 25, 2025, from https://en.wikipedia.org/wiki/Vergence-accommodation_conflict</ref> <ref name="DeliverContactsFocus">(2024-07-18) Exploring the Focal Distance in VR Headsets - Deliver Contacts. Retrieved April 25, 2025, from https://delivercontacts.com/blog/exploring-the-focal-distance-in-vr-headsets</ref> While the user's eyes converge appropriately for the virtual object's simulated distance (for example 0.5 meters), their eyes must maintain focus (accommodate) at the fixed optical distance of the display itself to keep the image sharp. This mismatch between the distance signaled by vergence and the distance signaled by accommodation is known as the '''[[vergence-accommodation conflict]]''' (VAC). <ref name="HoffmanVAC2008">Hoffman, D. M., Girshick, A. R., Akeley, K., & Banks, M. S. (2008). Vergence-accommodation conflicts hinder visual performance and cause visual fatigue. *Journal of Vision, 8*(3), 33. doi:10.1167/8.3.33</ref> <ref name="FacebookVAC2019">Facebook Research. (2019, March 28). *Vergence-Accommodation Conflict: Facebook Research Explains Why Varifocal Matters For Future VR*. YouTube. [https://www.youtube.com/watch?v=YWA4gVibKJE]</ref> <ref name="KramidaVAC2016">Kramida, Gregory. (2016). Resolving the vergence-accommodation conflict in head-mounted displays. *IEEE transactions on visualization and computer graphics, 22*(7), 1912-1931.</ref> | ||
The VAC forces the brain to deal with conflicting depth information, potentially leading to several issues: | The VAC forces the brain to deal with conflicting depth information, potentially leading to several issues: | ||
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To mitigate or eliminate the VAC and provide more accurate depth cues, researchers and companies are actively developing advanced display technologies: | To mitigate or eliminate the VAC and provide more accurate depth cues, researchers and companies are actively developing advanced display technologies: | ||
*'''[[Varifocal Displays]]''': These displays dynamically adjust the focal distance of the display optics (for example using physically moving lenses/screens, [[liquid lens]] technology, or [[deformable mirror]] devices) to match the simulated distance of the object the user is currently looking at. <ref name="KonradVAC2016">Konrad, R., Cooper, E. A., & Banks, M. S. (2016). Towards the next generation of virtual and augmented reality displays. *Optics Express, 24*(15), 16800-16809. doi:10.1364/OE.24.016800 | *'''[[Varifocal Displays]]''': These displays dynamically adjust the focal distance of the display optics (for example using physically moving lenses/screens, [[liquid lens]] technology, or [[deformable mirror]] devices) to match the simulated distance of the object the user is currently looking at. <ref name="KonradVAC2016">Konrad, R., Cooper, E. A., & Banks, M. S. (2016). Towards the next generation of virtual and augmented reality displays. *Optics Express, 24*(15), 16800-16809. doi:10.1364/OE.24.016800</ref> <ref name="DunnVarifocal2017">Dunn, David, et al. (2017). Wide field of view varifocal near-eye display using see-through deformable membrane mirrors. *IEEE transactions on visualization and computer graphics, 23*(4), 1322-1331.</ref> This typically requires fast and accurate [[eye tracking]] to determine the user's point of gaze and intended focus depth. Varifocal systems often simulate [[Depth of Field]] effects computationally, blurring parts of the scene not at the current focal distance. <ref name="ARInsiderVAC"/> Prototypes like Meta Reality Labs' "Half Dome" series have demonstrated this approach. <ref name="ARInsiderVAC"/> | ||
*'''[[Multifocal Displays]] (Multi-Plane Displays)''': Instead of a single, continuously adjusting focus, these displays present content on multiple discrete focal planes simultaneously or in rapid succession. <ref name="AkeleyMultifocal2004">Akeley, Kurt, Watt, S. J., Girshick, A. R., & Banks, M. S. (2004). A stereo display prototype with multiple focal distances. *ACM transactions on graphics (TOG), 23*(3), 804-813.</ref> The visual system can then accommodate to the plane closest to the target object's depth. Examples include stacked display panels or systems using switchable lenses. Magic Leap 1 used a two-plane system. <ref name="ARInsiderVAC"/> While reducing VAC, they can still exhibit quantization effects if an object lies between planes, and complexity increases with the number of planes. | *'''[[Multifocal Displays]] (Multi-Plane Displays)''': Instead of a single, continuously adjusting focus, these displays present content on multiple discrete focal planes simultaneously or in rapid succession. <ref name="AkeleyMultifocal2004">Akeley, Kurt, Watt, S. J., Girshick, A. R., & Banks, M. S. (2004). A stereo display prototype with multiple focal distances. *ACM transactions on graphics (TOG), 23*(3), 804-813.</ref> The visual system can then accommodate to the plane closest to the target object's depth. Examples include stacked display panels or systems using switchable lenses. Magic Leap 1 used a two-plane system. <ref name="ARInsiderVAC"/> While reducing VAC, they can still exhibit quantization effects if an object lies between planes, and complexity increases with the number of planes. | ||