In our daily lives, we are exposed to various stressors, which, even in mild forms, can lead to serious health issues when prolonged. Dance Movement Therapy (DMT) uses bodily movement as psychotherapy to improve health and well-being; however, traditional DMT requires therapists, specific setups, and physical props, limiting daily accessibility. To address this, we conducted a formative study with 10 DMT experts and developed ImmersiveDMT, a VR application that provides real-time visual and auditory feedback in response to users’ movements. A user study with 56 participants examined how visual, auditory, and audiovisual feedback affect expressive movement and stress reduction compared to a non-responsive immersive baseline. Results showed that auditory and audiovisual conditions induced significantly more expressive movement compared to baseline. Both visual and auditory feedback achieved significant stress reduction below baseline (V: 17.1%, p=.004; A: 16.6%, p=.042), while combined audiovisual feedback led to less stress reduction. This research presents a novel approach to accessible daily stress management by integrating VR and DMT, demonstrating new possibilities for self-directed mental health support.

Conventional Augmented Reality (AR) head-mounted displays (HMDs) integrate all essential components within the wearable unit, imposing limitations on weight, heat dissipation, and battery life. Beaming Displays (BDs) address these constraints by externalizing computation and projection; however, achieving reliable low-latency six-degrees-of-freedom (6-DoF) tracking remains a challenge. We present BeamStellar, a BD system that enables low-latency 6-DoF head tracking by combining a position-sensitive detector (PSD) with a spatio-temporally modulated infrared LED array mounted on passive glasses. The system integrates tracking and projection via a co-aligned optical path and performs real-time signal processing on an FPGA to minimize tracking latency. We describe the system architecture, pose reconstruction pipeline, and evaluate the pose-tracking latency of approximately 430 µs. BeamStellar provides a replicable, lightweight AR tracking platform, establishing a new paradigm for low-latency environment-based AR systems.

Augmented Reality (AR) glasses must be slim, lightweight, and energy-efficient to achieve widespread adoption. Beaming Displays present a promising solution by offloading active components, such as the power-supplied light engine, into the surrounding environment while leaving only passive elements, like the eyepiece, in the wearable device. However, existing approaches still struggle to achieve both a slim design and a wide tolerance for projection angles relative to the user’s head orientation. In this work, we introduce a design for light-receiving glasses using a diffractive waveguide with in-coupling and out-coupling gratings. Our approach expands the allowable range of incident angles while maintaining a compact, lightweight form factor. We developed a proof-of-concept prototype and demonstrated an incident angle tolerance of approximately 20-30 degrees range, overcoming the previous design of 5 degrees.

Gaze guidance is essential for directing user attention to specific areas of interest. However, conventional visual cues generate persistent visual noise that hinders concentration during tasks. We propose Saccaidance, a gaze-guidance method that appears only when users move their gaze. Saccaidance employs temporal additive color mixing and 480 Hz high-speed displays to shift the color phase of guidance patterns. This renders the patterns barely visible during fixation and makes them appear transiently when users move their gaze as a color-breaking effect. This intermittent gaze guidance appears only during gaze transitions, providing effective guidance without interfering with focused work or requiring eye-tracking hardware. We conducted experiments with 24 participants under four conditions that involved search tasks: an unmodified baseline, conventional explicit guidance, and our proposed method using oval and radial patterns. The results show that our approach effectively constrains the exploration area while preserving subjective naturalness. We also outline application scenarios of our method, including document highlighting.

Systems with occlusion capabilities, such as those used in vision augmentation, image processing, and optical see-through head-mounted display (OST-HMD), have gained popularity. Achieving precise (hard-edge) occlusion in these systems is challenging, often requiring complex optical designs and bulky volumes. On the other hand, utilizing a single transparent liquid crystal display (LCD) is a simple approach to create occlusion masks. However, the generated mask will appear defocused (soft-edge) resulting in insufficient blocking or occlusion leakage. In our work, we delve into the perception of soft-edge occlusion by the human visual system and present a preference-based optimal expansion method that minimizes perceived occlusion leakage. In a user study involving 20 participants, we made a noteworthy observation that the human eye perceives a sharper edge blur of the occlusion mask when individuals see through it and gaze at a far distance, in contrast to the camera system's observation. Moreover, our study revealed significant individual differences in the perception of soft-edge masks in human vision when focusing. These differences may lead to varying degrees of demand for mask size among individuals. Our evaluation demonstrates that our method successfully accounts for individual differences and achieves optimal masking effects at arbitrary distances and pupil sizes.

Visual guidance (VG) plays an essential role in directing user attention in virtual reality (VR) and augmented reality (AR) environments. However, traditional approaches rely on explicit visual annotations, which often compromise visual clarity and increase user cognitive load. To address this issue, we propose an unobtrusive VG technique based on color vibration, a phenomenon in which rapidly alternating colors at frequencies above 25 Hz are perceived as a single intermediate color. Our work explores a perceptual state that exists between complete color fusion and visible flicker, where color differences remain detectable without conscious awareness of vibration. Through two experimental studies, we first identified the thresholds separating complete fusion, this intermediate perceptual state, and visible flicker by systematically varying color vibration parameters. Subsequently, we applied color vibrations with derived thresholds to natural image regions and validated their attention-guiding capabilities using eye-tracking measurements. The results demonstrate that controlled color vibration successfully directs user attention while maintaining low cognitive demand, providing an effective method for implementing unobtrusive VG in VR and AR systems.

Juiciness is visual pizzazz used to improve player experience and engagement in games. Most research has focused on juicy particle effects. However, text effects are also commonly used in games, albeit not always juiced up. One type is onomatopoeia, a well-defined element of human language that has been translated to visual media, such as comic books and games. Another is semantic text, often used to provide performance feedback in games. In this work, we explored the relationship between juiciness and text effects, aiming to replicate juicy user experiences with text-based juice and combining particle and text juice. We show in a multi-phase within-subjects experiment that users rate juicy text effects similarly to particles effects, with comparable performance, and more reliable feedback. We also hint at potential improvement in user experience when both are combined, and how text stimuli may be perceived differently than other visual ones. We contribute empirical findings on the juicy-text connection in the context of visual effects for interactive media.

Light Attenuation Displays (LADs), a subset of Optical See-Through Head-Mounted Displays (OST-HMDs), enable image display in bright environments by filtering incident light at the pixel level. Although recent methods have proposed single-DMD light attenuation, they do not consider additive color display and background compensation, limiting their applicability in real-world scenarios. We present FactoredSweeper, a single digital micromirror device (DMD) system that incorporates both light attenuation and addition. By synchronizing the DMD, color filter, and light source, our system generates an additive virtual image, light attenuation, and occlusion through time multiplexing. To produce the target image while compensating for the background, we optimize time-multiplexed binary DMD patterns and LED/color filter schedules using perceptually-driven non-negative matrix factorization. Simulations and prototypes demonstrate that our integrated attenuation-addition single-SLM system achieves superior dynamic range and perceptual image quality compared to conventional occlusion-capable OST-HMDs using grayscale occlusion masks.

We are pleased to present the proceedings of the 31st IEEE Conference on Virtual Reality and 3D User Interfaces (IEEE VR 2024), held March 16–21, 2024, in Orlando, Florida, US, in on-site format. These proceedings contain 101 of the 180 IEEE VR 2024 papers, with the other 79 papers being published in the IEEE VR 2024 special issue of the Transactions on Visualization and Computer Graphics. IEEE VR 2024 had 627 submissions for an acceptance rate of 101/627=16.1% as conference papers, or 180/627=28.7% when including the journal papers.

Existing near-eye displays (NEDs) have trade-offs related to size, weight, computational resources, battery life, and body temperature. A recent paradigm, beaming display, addresses these trade-offs by separating the NED into a steering projector (SP) for image presentation and a passive headset worn by the user. However, the beaming display has issues with the projection area of a single SP and has severe limitations on the head orientation and pose that the user can move. In this study, we distribute dual steering projectors in the scene to extend the head orientation and pose of the beaming display by coordinating the dual projections on a passive headset. For cooperative control of each SP, we define a geometric model of the SPs and propose a calibration and projection control method designed for multiple projectors. We present implementations of the system along with evaluations showing that the precision and delay are 1.8 ∼ 5.7 mm and 14.46 ms, respectively, at a distance of about 1 m from the SPs. From this result, our prototype with multiple SPs can project images in the projection area ($20\ \text{mm} \times 30\ \text{mm}$) of the passive headset while extending the projectable head orientation. Furthermore, as applications of cooperative control by multiple SPs, we show the possibility of multiple users, improving dynamic range and binocular presentation.

Light Attenuation Displays (LADs) are a type of Optical See-Through Head-Mounted Display (OST-HMD) that present images by attenuating incoming light with a pixel-wise polarizing color filter. Although LADs can display images in bright environments, there is a trade-off between the number of Spatial Light Modulators (SLMs) and the color gamut and contrast that can be expressed, making it difficult to achieve both high-fidelity image display and a small form factor. To address this problem, we propose StainedSweeper, a LAD that achieves both the wide color gamut and the variable intensity with a single SLM. Our system synchronously controls a pixel-wise Digital Micromirror Device (DMD) and a nonpixel polarizing color filter to pass light when each pixel is the desired color. By sweeping this control at high speed, the human eye perceives images in a time-multiplexed, integrated manner. To achieve this, we develop the OST-HMD design using a reflective Solc filter as a polarized color filter and a color reproduction algorithm based on the optimization of the time-multiplexing matrix for the selected primary color filters. Our proof-of-concept prototype showed that our single SLM design can produce subtractive images with variable contrast and a wider color gamut than conventional LADs.

In this special issue ofIEEE Transactions on Visualization and Computer Graphics(TVCG), we are pleased to present the top papers from the 31th IEEE Conference on Virtual Reality and 3D User Interfaces (IEEE VR 2024), held March 16-21, 2024, in Orlando, Florida, US.

We propose HaptoFloater, a low-latency mid-air visuo-haptic augmented reality (VHAR) system that utilizes imperceptible color vibrations. When adding tactile stimuli to the visual information of a mid-air image, the user should not perceive the latency between the tactile and visual information. However, conventional tactile presentation methods for mid-air images, based on camera-detected fingertip positioning, introduce latency due to image processing and communication. To mitigate this latency, we use a color vibration technique; humans cannot perceive the vibration when the display alternates between two different color stimuli at a frequency of 25 Hz or higher. In our system, we embed this imperceptible color vibration into the mid-air image formed by a micromirror array plate, and a photodiode on the fingertip device directly detects this color vibration to provide tactile stimulation. Thus, our system allows for the tactile perception of multiple patterns on a mid-air image in 59.5 ms. In addition, we evaluate the visual-haptic delay tolerance on a mid-air display using our VHAR system and a tactile actuator with a single pattern and faster response time. The results of our user study indicate a visual-haptic delay tolerance of 110.6 ms, which is considerably larger than the latency associated with systems using multiple tactile patterns.

The tactile sensation of textiles is critical in determining the comfort of clothing. For remote use, such as online shopping, users cannot physically touch the textile of clothes, making it difficult to evaluate its tactile sensation. Tactile sensing and actuation devices are required to transmit the tactile sensation of textiles. The sensing device needs to recognize different garments, even with hand-held sensors. In addition, the existing actuation device can only present a limited number of known patterns and cannot transmit unknown tactile sensations of textiles. To address these issues, we propose Telextiles, an interface that can remotely transmit tactile sensations of textiles by creating a latent space that reflects the proximity of textiles through contrastive self-supervised learning. We confirm that textiles with similar tactile features are located close to each other in the latent space through a two-dimensional plot. We then compress the latent features for known textile samples into the 1D distance and apply the 16 textile samples to the rollers in the order of the distance. The roller is rotated to select the textile with the closest feature if an unknown textile is detected.

An emerging alternative to conventional Augmented Reality (AR) glasses designs, Beaming displays promise slim AR glasses free from challenging design trade-offs, including battery-related limits or computational budget-related issues. These beaming displays remove active components such as batteries and electronics from AR glasses and move them to a projector that projects images to a user from a distance (1–2 meters), where users wear only passive optical eyepieces. However, earlier implementations of these displays delivered poor resolutions (7 cycles per degree) without any optical focus cues and were introduced with a bulky form-factor eyepiece ($\sim 50\ mm$thick). This paper introduces a new milestone for beaming displays, which we call HoloBeam. In this new design, a custom holographic projector populates a micro-volume located at some distance (1–2 meters) with multiple planes of images. Users view magnified copies of these images from this small volume with the help of an eyepiece that is either a Holographic Optical Element (HOE) or a set of lenses. Our HoloBeam prototypes demonstrate the thinnest AR glasses to date with submillimeter thickness (e.g., HOE film is only$120\ \mu m$thick). In addition, HoloBeam prototypes demonstrate near retinal resolutions (24 cycles per degree) with a 70 degrees-wide field of view.

This paper introduces a new multiplane CGH computation method to reconstruct artifact-free high-quality holograms with natural-looking defocus blur. Our method introduces a new targeting scheme and a new loss function. While the targeting scheme accounts for defocused parts of the scene at each depth plane, the new loss function analyzes focused and defocused parts separately in reconstructed images. Our method support phase-only CGH calculations using various iterative (e.g., Gerchberg-Saxton, Gradient Descent) and non-iterative (e.g., Double Phase) CGH techniques. We achieve our best image quality using a modified gradient descent-based optimization recipe where we introduce a constraint inspired by the double phase method. We validate our method experimentally using our proof-of-concept holographic display, comparing various algorithms, including multi-depth scenes with sparse and dense contents.

Occlusion is a crucial visual element in optical see-through (OST) augmented reality, however, implementing occlusion in OST displays while addressing various design trade-offs is a difficult problem. In contrast to the traditional method of using spatial light modulators (SLMs) for the occlusion mask, using photochromic materials as occlusion masks can effectively eliminate diffraction artifacts in see-through views due to the lack of electronic pixels, thus providing superior see-through image quality. However, this design requires UV illumination to activate the photochromic mate-rial, which traditionally requires multiple SLMs, resulting in a larger form factor for the system. This paper presents a compact photochromic occlusion-capable OST design using multilayer, wavelength-dependent holographic optical lenses (HOLs). Our approach employs a single digital mi-cromirror display (DMD) to form both the occlusion mask with UV light and a virtual image with visible light in a time-multiplexed man-ner. We demonstrate our proof-of-concept system on a bench-top setup and assess the appearance and contrasts of the displayed image. We also suggest potential improvements for current prototypes to encourage the community to explore this occlusion approach.

This paper introduces Retinal Homing Display, which presents focus-free stereoscopic images via retinal projection, thus eliminating the need for the user to wear additional equipment. Traditional 3D displays, typically classified as either naked-eye stereoscopic or wearable, present inherent challenges: the former involves a compromise between resolution and accurate depth perception, while the latter imposes an additional burden on the user. Our proposed display employs optical and mechanical mechanisms to converge projector light at the user’s pupil center, simultaneously tracking eye movements. This lets the user perceive focus-free, high-resolution stereoscopic images without wearable equipment. We implemented a proof-of-concept system utilizing a robotic arm and a Dihedral Corner Reflector Array (DCRA), subsequently evaluating image quality and its eyebox. Finally, we discuss the limitations of the current prototype and outline potential directions for future research.

This paper presents a low-latency Beaming Display system with a 133 μs motion-to-photon (M2P) latency, the delay from head motion to the corresponding image motion. The Beaming Display represents a recent near-eye display paradigm that involves a steerable remote projector and a passive wearable headset. This system aims to overcome typical trade-offs of Optical See-Through Head-Mounted Displays (OST-HMDs), such as weight and computational resources. However, since the Beaming Display projects a small image onto a moving, distant viewpoint, M2P latency significantly affects displacement. To reduce M2P latency, we propose a low-latency Beaming Display system that can be modularized without relying on expensive high-speed devices. In our system, a 2D position sensor, which is placed coaxially on the projector, detects the light from the IR-LED on the headset and generates a differential signal for tracking. An analog closed-loop control of the steering mirror based on this signal continuously projects images onto the headset. We have implemented a proof-of-concept prototype, evaluated the latency and the augmented reality experience through a user-perspective camera, and discussed the limitations and potential improvements of the prototype.

This work integrates Schlieren Imaging, a unique sensing modality, into Augmented Reality (AR) to explore ways to utilize invisible airflows for AR. Schlieren imaging is an imaging technique that visualizes the flow of fluids, which is normally invisible to the eyes. Theoretically, the technique can calculate the motion, pressure, temperature, and density of the airflow in our physical world. This unique, but less applied modality may expand interaction paradigms in AR and VR. We build a proof-of-concept AR system combined with Schlieren imaging that allows real airflow to affect virtual objects. The results of quantitative analyses show that our system can integrate different types of airflow with pressure values ranging from weak breathing actions to a heat gun up to 10m/s or 0.25m3/min airflow. We also showcase AR use cases including blowing out a virtual candle and a heat gun.

Augmented Reality has traditionally been used to display digital overlays in real environments. Many AR applications such as remote collaboration, picking tasks, or navigation require highlighting physical objects for selection or guidance. These highlights use graphical cues such as outlines and arrows. Whilst effective, they greatly contribute to visual clutter, possibly occlude scene elements, and can be problematic for long-term use. Substituting those overlays, we explore saliency modulation to accentuate objects in the real environment to guide the user’s gaze. Instead of manipulating video streams, like done in perception and cognition research, we investigate saliency modulation of the real world using optical-see-through head-mounted displays. This is a new challenge, since we do not have full control over the view of the real environment. In this work we provide our specific solution to this challenge, including built prototypes and their evaluation.

While presenting a photorealistic appearance plays a major role in immersion in Augmented Virtuality environment, displaying that of real objects remains a challenge. Recent developments in photogrammetry have facilitated the incorporation of real objects into virtual space. However, reproducing complex appearances, such as subsurface scattering and transparency, still requires a dedicated environment for measurement and possesses a trade-off between rendering quality and frame rate.

The fundamental goal of augmented reality (AR) is to integrate virtual objects into the user’s perceived reality seamlessly. However, various issues hinder this integration. In particular, Optical See Through (OST) AR is hampered by the need for light subtraction due to its see-through nature, making some basic rendering harder to realize. In this paper, we realize mutual shadows between real and virtual objects in OST AR to improve this virtual-real integration. Shadows are a classic problem in computer graphics, virtual reality, and video see-through AR, yet they have not been fully explored in OST AR due to the light subtraction requirement. We build a proof-of-concept system that combines a custom occlusion-capable OST display, global light source estimation, 3D registration, and ray-tracing-based rendering. We will demonstrate mutual shadows using a prototype and demonstrate its effectiveness by quantitatively evaluating shadows with the real environment using a perceptual visual metric.

Augmented Human (AH) is a research field enhancing human physical abilities or supporting human activity using advanced technologies. As one of the AH approaches, previous studies have attached an actuator to a human body or tools used for an activity. The attached actuators are used to control their movements to support an activity. In this study, instead of attaching actuators, we propose to directly apply noncontact ultrasound force to a lightweight tool to manipulate it. The advantage of using noncontact force is that users do not need to wear a specific device and to process tools used for the activity. As a proof-of-concept system, we developed an ultrasound-based curveball system by which table tennis players can shoot a curveball regardless of their physical ability. In the system, a moving ping-pong ball (PPB) is a target tool for remote manipulation. The system curves the trajectory of a moving PPB by continuously focusing ultrasound on it. Users can control the curve timing and the curve direction (left or right) using a racket-shaped controller. In the user study, we conducted an actual table tennis match using the curveball system and qualitatively confirmed that the player using the system had the upper hand. Another user study using a ball dispenser quantitatively showed that the ultrasound-driven curveball increased the number of mistakes of the opponent player 2.95 times. These results indicate that the proposed concept is feasible.

Existing near-eye display designs struggle to balance between multiple trade-offs such as form factor, weight, computational requirements, and battery life. These design trade-offs are major obstacles on the path towards an all-day usable near-eye display. In this work, we address these trade-offs by, paradoxically, removing the display from near-eye displays. We present the beaming displays, a new type of near-eye display system that uses a projector and an all passive wearable headset. We modify an off-the-shelf projector with additional lenses. We install such a projector to the environment to beam images from a distance to a passive wearable headset. The beaming projection system tracks the current position of a wearable headset to project distortion-free images with correct perspectives. In our system, a wearable headset guides the beamed images to a user's retina, which are then perceived as an augmented scene within a user's field of view. In addition to providing the system design of the beaming display, we provide a physical prototype and show that the beaming display can provide resolutions as high as consumer-level near-eye displays. We also discuss the different aspects of the design space for our proposal.

We present computational phase-modulated eyeglasses, a see-through optical system that modulates the view of the user using phase-only spatial light modulators (PSLM). A PSLM is a programmable reflective device that can selectively retardate, or delay, the incoming light rays. As a result, a PSLM works as a computational dynamic lens device. We demonstrate our computational phase-modulated eyeglasses with either a single PSLM or dual PSLMs and show that the concept can realize various optical operations including focus correction, bi-focus, image shift, and field of view manipulation, namely optical zoom. Compared to other programmable optics, computational phase-modulated eyeglasses have the advantage in terms of its versatility. In addition, we also presents some prototypical focus-loop applications where the lens is dynamically optimized based on distances of objects observed by a scene camera. We further discuss the implementation, applications but also discuss limitations of the current prototypes and remaining issues that need to be addressed in future research.

Commonly used Head Mounted Displays (HMDs) in Augmented Reality (AR), namely Optical See-Through (OST) displays, suffer from a main drawback: their focal lenses can only provide a fixed focal distance. Such a limitation is suspected to be one of the main factors for distance misperception in AR. In this paper, we studied the use of an emerging new kind of AR display to tackle such perception issues: Retinal Projection Displays (RPDs). With RPDs, virtual images have no focal distance and the AR content is always in focus. We conducted the first reported experiment evaluating egocentric distance perception of observers using Retinal Projection Displays. We compared the precision and accuracy of the depth estimation between real and virtual targets, displayed by either OST HMDs or RPDs. Interestingly, our results show that RPDs provide depth estimates in AR closer to real ones compared to OST HMDs. Indeed, the use of an OST device was found to lead to an overestimation of the perceived distance by 16%, whereas the distance overestimation bias dropped to 4% with RPDs. Besides, the task was reported with the same level of difficulty and no difference in precision. As such, our results shed the first light on retinal projection displays' benefits in terms of user's perception in Augmented Reality, suggesting that RPD is a promising technology for AR applications in which an accurate distance perception is required.

We present StainedView, an optical see-through display that spatially filters the spectral distribution of light to form an image with improved color fidelity. Existing light-attenuation displays have limited color fidelity and contrast, resulting in a degraded appearance of virtual images. To use these displays to present virtual images that are more consistent with the real world, we require three things: intensity modulation of incoming light, spatial color filtering with narrower bandwidth, and appropriate light modulation for incoming light with an arbitrary spectral distribution. In StainedView, we address the three requirements by cascading two phase-only spatial light modulators (PSLMs), a digital micromirror device, and polarization optics to control both light intensity and spectrum distribution. We show that our design has a 1.8 times wider color gamut fidelity (75.8% fulfillment of sRGB color space) compared to the existing single-PSLM approach (41.4%) under a reference white light. We demonstrated the design with a proof-of-concept display system. We further introduce our optics design and pixel-selection algorithm for the given light input, evaluate the spatial color filter, and discuss the limitation of the current prototype.

This paper presents CoSummary, an adaptive video fast-forwarding technique for browsing surgical videos recorded by wearable cameras. Current wearable technologies allow us to record complex surgical skills, however, an efficient browsing technique for these videos is not well established. In order to assist browsing surgical videos, our study focuses on adaptively changing playback speeds through the learning and detecting collaborative scenes based on surgeon hand placement and gaze information. Our evaluation shows that the proposed method is able to highlight important collaborative scenes and skip less important scenes during surgical procedures. We have also performed a subjective study with surgeons in order to have professional feedback. The results confirmed the effectiveness of the proposed method in comparison to uniform video fast-forwarding.

Physically moving real objects via a computational force connects computers and the real world and has been applied to tangible interfaces and mid-air display. Many researchers have controlled only a stationary real object by computational force. On the other hand, controlling a moving object can expand the real space that is controllable by the computer. In this paper, we explore the potential of computational force from the viewpoint of changing the trajectory of a moving object. Changing the trajectory is the primitive model to control a moving object, and it is the technological challenge requiring high-speed measurement and non-contact force with high-spatial resolution. As a proof-of-concept, we introduce Hopping-Pong changing the trajectory of a flying Ping-Pong Ball (PPB) using ultrasound force. The result shows that Hopping-Pong changes the trajectory of a PPB 344 mm. We conclude that a computational force is capable of controlling a moving object in the real world. This research contributes to expanding the computationally controlled space with applications for augmented sports, HCI and factory automation.

We propose a varifocal occlusion technique for optical see-through head-mounted displays (OST-HMDs). Occlusion in OST-HMDs is a powerful visual cue that enables depth perception in augmented reality (AR). Without occlusion, virtual objects rendered by an OST-HMD appear semi-transparent and less realistic. A common occlusion technique is to use spatial light modulators (SLMs) to block incoming light rays at each pixel on the SLM selectively. However, most of the existing methods create an occlusion mask only at a single, fixed depth-typically at infinity. With recent advances in varifocal OST-HMDs, such traditional fixed-focus occlusion causes a mismatch in depth between the occlusion mask plane and the virtual object to be occluded, leading to an uncomfortable user experience with blurred occlusion masks. In this paper, we thus propose an OST-HMD system with varifocal occlusion capability: we physically slide a transmissive liquid crystal display (LCD) to optically shift the occlusion plane along the optical path so that the mask appears sharp and aligns to a virtual image at a given depth. Our solution has several benefits over existing varifocal occlusion methods: it is computationally less demanding and, more importantly, it is optically consistent, i.e., when a user loses focus on the corresponding virtual image, the mask again gets blurred consistently as the virtual image does. In the experiment, we build a proof-of-concept varifocal occlusion system implemented with a custom retinal projection display and demonstrate that the system can shift the occlusion plane to depths ranging from 25 cm to infinity.

We present a display for optical see-through near-eye displays based on light attenuation, a new paradigm that forms images by spatially subtracting colors of light. Existing optical see-through head-mounted displays (OST-HMDs) form virtual images in an additive manner-they optically combine the light from an embedded light source such as a microdisplay into the users' field of view (FoV). Instead, our light attenuation display filters the color of the real background light pixel-wise in the users' see-through view, resulting in an image as a spatial color filter. Our image formation is complementary to existing light-additive OST-HMDs. The core optical component in our system is a phase-only spatial light modulator (PSLM), a liquid crystal module that can control the phase of the light in each pixel. By combining PSLMs with polarization optics, our system realizes a spatially programmable color filter. In this paper, we introduce our optics design, evaluate the spatial color filter, consider applications including image rendering and FoV color control, and discuss the limitations of the current prototype.

Prescription glasses are used by many people as a simple, and even fashionable way, to correct refractive problems of the eye. However, there are other visual impairments that cannot be treated with an optical lens in conventional glasses. In this work we present ChromaGlasses, Computational Glasses using optical head-mounted displays for compensating colour vision deficiency. Unlike prior work that required users to look at a screen in their visual periphery rather than at the environment directly, ChromaGlasses allow users to directly see the environment using a novel head-mounted displays design that analyzes the environment in real-time and changes the appearance of the environment with pixel precision to compensate the impairment of the user. In this work, we present first prototypes for ChromaGlasses and report on the results from several studies showing that ChromaGlasses are an effective method for managing colour blindness.

The photo reflective sensor (PRS), a tiny distant-measurement module, is a popular electronic component widely used in wearable user-interfaces. An unavoidable issue of such wearable PRS devices in practical use is the need of user-independent training to have high gesture recognition accuracy. Each new user has to re-train a device by providing new training data (we call the inter-user setup). Even worse, re-training is also necessary ideally every time when the same user re-wears the device (we call the intra-user setup). In this paper, we propose a domain adaptation framework to reduce this training cost of users. Specifically, we adapt a pre-trained convolutional neural network (CNN) for both inter-user and intra-user setups to maintain the recognition accuracy high. We demonstrate, with an actual PRS device, that our framework significantly improves the average classification accuracy of the intra-user and inter-user setups up to 87.43% and 80.06% against the baseline (non-adapted) setups with the accuracy 68.96% and 63.26% respectively.

Interactive surfaces and spaces (ISS) research has been advanced by augmented reality (AR) display technologies. Recent trends of computational displays overcome limitations of existing display technologies by optimizing both hardware and software while considering human perception. We plan to held a workshop on computational AR displays (CARD) to explore emerging ISS research issues by promoting communications and interactions between ISS and CARD communities.

Optical see-through head-mounted displays (OST HMDs) are a major output medium for Augmented Reality, which have seen significant growth in popularity and usage among the general public due to the growing release of consumer-oriented models, such as the Microsoft Hololens. Unlike Virtual Reality headsets, OST HMDs inherently support the addition of computer-generated graphics directly into the light path between a user's eyes and their view of the physical world. As with most Augmented and Virtual Reality systems, the physical position of an OST HMD is typically determined by an external or embedded 6-Degree-of-Freedom tracking system. However, in order to properly render virtual objects, which are perceived as spatially aligned with the physical environment, it is also necessary to accurately measure the position of the user's eyes within the tracking system's coordinate frame. For over 20 years, researchers have proposed various calibration methods to determine this needed eye position. However, to date, there has not been a comprehensive overview of these procedures and their requirements. Hence, this paper surveys the field of calibration methods for OST HMDs. Specifically, it provides insights into the fundamentals of calibration techniques, and presents an overview of both manual and automatic approaches, as well as evaluation methods and metrics. Finally, it also identifies opportunities for future research.

Spatial augmented reality (SAR) pursues realism in rendering materials and objects. To advance this goal, we propose a hybrid SAR (HySAR) that combines a projector with optical see-through head-mounted displays (OST-HMD). In an ordinary SAR scenario with co-located viewers, the viewers perceive the same virtual material on physical surfaces. In general, the material consists of two components: a view-independent (VI) component such as diffuse reflection, and a view-dependent (VD) component such as specular reflection. The VI component is static over viewpoints, whereas the VD should change for each viewpoint even if a projector can simulate only one viewpoint at one time. In HySAR, a projector only renders the static VI components. In addition, the OST-HMD renders the dynamic VD components according to the viewer's current viewpoint. Unlike conventional SAR, the HySAR concept theoretically allows an unlimited number of co-located viewers to see the correct material over different viewpoints. Furthermore, the combination enhances the total dynamic range, the maximum intensity, and the resolution of perceived materials. With proof-of-concept systems, we demonstrate HySAR both qualitatively and quantitatively with real objects. First, we demonstrate HySAR by rendering synthetic material properties on a real object from different viewpoints. Our quantitative evaluation shows that our system increases the dynamic range by 2.24 times and the maximum intensity by 2.12 times compared to an ordinary SAR system. Second, we replicate the material properties of a real object by SAR and HySAR, and show that HySAR outperforms SAR in rendering VD specular components.

Airborne Ultrasound Tactile Displays (AUTD) are tactile displays that can generate vibrotactile sensation on human skin. Combining an AUTD with a projector-camera system, it is possible to present synchronous visual and haptic stimuli that is physically aligned in the 3D space. To maintain the synchronous sensation as realistic as possible, an accurate crucial to spatial calibration between the AUTD and the projector-camera system is required. This paper thereby proposes a calibration method for the AUTD system by utilizing fur material to recognize the output focal points of an AUTD in the camera coordinate system. Our method simplifies the calibration procedure with calibration error of 2.63 mm.

We propose a hybrid SAR concept combining a projector and Optical See-Through Head-Mounted Displays (OST-HMD). Our proposed hybrid SAR system utilizes OST-HMD as an extra rendering layer to render a view-dependent property in OST-HMDs according to the viewer's viewpoint. Combined with view-independent components created by a static projector, the viewer can see richer material contents. Unlike conventional SAR systems, our system theoretically allows unlimited number of viewers seeing enhanced contents in the same space while keeping the existing SAR experiences. Furthermore, the system enhances the total dynamic range, the maximum intensity, and the resolution of perceived materials. With a proof-of-concept system that consists of a projector and an OST-HMD, we qualitatively demonstrate that our system successfully creates hybrid rendering on a hemisphere object from five horizontal viewpoints. Our quantitative evaluation also shows that our system increases the dynamic range by 2.1 times and the maximum intensity by 1.9 times compared to an ordinary SAR system.

We present a method for focal distance estimation of a freely-orienting eye using Purkinje-Sanson (PS) images, which are reflections of light on the inner structures of the eye. Using an infrared camera with a rigidly-fixed LED, our method creates an estimation model based on 3D gaze and the distance between reflections in the PS images that occur on the corneal surface and anterior surface of the eye lens. The distance between these two reflections changes with focus, so we associate that information to the focal distance on a user. Unlike conventional methods that mainly relies on 2D pupil size which is sensitive to scene lighting and the fourth PS image, our method detects the third PS image which is more representative of accommodation. Our feasibility study on a single user with a focal range from 15–45 cm shows that our method achieves mean and median absolute errors of 3.15 and 1.93 cm for a 10-degree viewing angle. The study shows that our method is also tolerant against environment lighting changes.

We propose a facial expression mapping technology between virtual avatars and Head-Mounted Display (HMD) users. HMD allow people to enjoy an immersive Virtual Reality (VR) experience. A virtual avatar can be a representative of the user in the virtual environment. However, the synchronization of the the virtual avatar's expressions with those of the HMD user is limited. The major problem of wearing an HMD is that a large portion of the user's face is occluded, making facial recognition difficult in an HMD-based virtual environment. To overcome this problem, we propose a facial expression mapping technology using retro-reflective photoelectric sensors. The sensors attached inside the HMD measures the distance between the sensors and the user's face. The distance values of five basic facial expressions (Neutral, Happy, Angry, Surprised, and Sad) are used for training the neural network to estimate the facial expression of a user. We achieved an overall accuracy of 88% in recognizing the facial expressions. Our system can also reproduce facial expression change in real-time through an existing avatar using regression. Consequently, our system enables estimation and reconstruction of facial expressions that correspond to the user's emotional changes.

We propose an occlusion compensation method for optical see-through head-mounted displays (OST-HMDs) equipped with a singlelayer transmissive spatial light modulator (SLM), in particular, a liquid crystal display (LCD). Occlusion is an important depth cue for 3D perception, yet realizing it on OST-HMDs is particularly difficult due to the displays' semitransparent nature. A key component for the occlusion support is the SLM-a device that can selectively interfere with light rays passing through it. For example, an LCD is a transmissive SLM that can block or pass incoming light rays by turning pixels black or transparent. A straightforward solution places an LCD in front of an OST-HMD and drives the LCD to block light rays that could pass through rendered virtual objects at the viewpoint. This simple approach is, however, defective due to the depth mismatch between the LCD panel and the virtual objects, leading to blurred occlusion. This led existing OST-HMDs to employ dedicated hardware such as focus optics and multi-stacked SLMs. Contrary to these viable, yet complex and/or computationally expensive solutions, we return to the single-layer LCD approach for the hardware simplicity while maintaining fine occlusion-we compensate for a degraded occlusion area by overlaying a compensation image. We compute the image based on the HMD parameters and the background scene captured by a scene camera. The evaluation demonstrates that the proposed method reduced the occlusion leak error by 61.4% and the occlusion error by 85.7%.

For neurodegenerative conditions like Parkinson's disease, early and accurate diagnosis is still a difficult task. Evaluations can be time consuming, patients must often travel to metropolitan areas or different cities to see experts, and misdiagnosis can result in improper treatment. To date, only a handful of assistive or remote methods exist to help physicians evaluate patients with suspected neurological disease in a convenient and consistent way. In this paper, we present a low-cost VR interface designed to support evaluation and diagnosis of neurodegenerative disease and test its use in a clinical setting. Using a commercially available VR display with an infrared camera integrated into the lens, we have constructed a 3D virtual environment designed to emulate common tasks used to evaluate patients, such as fixating on a point, conducting smooth pursuit of an object, or executing saccades. These virtual tasks are designed to elicit eye movements commonly associated with neurodegenerative disease, such as abnormal saccades, square wave jerks, and ocular tremor. Next, we conducted experiments with 9 patients with a diagnosis of Parkinson's disease and 7 healthy controls to test the system's potential to emulate tasks for clinical diagnosis. We then applied eye tracking algorithms and image enhancement to the eye recordings taken during the experiment and conducted a short follow-up study with two physicians for evaluation. Results showed that our VR interface was able to elicit five common types of movements usable for evaluation, physicians were able to confirm three out of four abnormalities, and visualizations were rated as potentially useful for diagnosis.

In this paper, we present a wearable facial expression recognition system that can analyse and enhance a daily experience. Our aim is to create a mindful experience in daily life by connecting the device with everyday objects and service. To this end, we made two prototypes that supports users to keep right side of emotions: 1) a text chatting system that automatically inserts an emoticon based on his/her facial expressions in the end of a comment a user typed, 2) a plant interface controlled by facial expressions. We also analysed multiple users' facial expressions while they played video games. We confirmed that visualization of sensor data from the device shows the possibility for estimating the transition of different facial expressions.

Properly calibrating an optical see-through head-mounted display (OST-HMD) and maintaining a consistent calibration over time can be a very challenging task. Automated methods need an accurate model of both the OST-HMD screen and the user's constantly changing eye-position to correctly project virtual information. While some automated methods exist, they often have restrictions, including fixed eye-cameras that cannot be adjusted for different users.To address this problem, we have developed a method that automatically determines the position of an adjustable eye-tracking camera and its unconstrained position relative to the display. Unlike methods that require a fixed pose between the HMD and eye camera, our framework allows for automatic calibration even after adjustments of the camera to a particular individual's eye and even after the HMD moves on the user's face. Using two sets of IR-LEDs rigidly attached to the camera and OST-HMD frame, we can calculate the correct projection for different eye positions in real time and changes in HMD position within several frames. To verify the accuracy of our method, we conducted two experiments with a commercial HMD by calibrating a number of different eye and camera positions. Ground truth was measured through markers on both the camera and HMD screens, and we achieve a viewing accuracy of 1.66 degrees for the eyes of 5 different experiment participants.

We present an off-the-shelf, low-latency Optical See-through Head-Mounted Displays (OST-HMD) for Augmented Reality (AR). Temporally consistent visualization is crucial for realizing immersive AR experiences. This is challenging since it requires both accurate head-tracking and low-latency rendering of AR content. Building a system which meets both constraints usually requires experts on computer vision/graphics and expensive display hardware. This work demonstrates that such high spatio-temporal fidelity is achievable with commodity hardware available today. We build a custom OST-HMD system that consists of a virtual reality HMD, i.e., the Oculus Rift DK2, and half-mirror optics, and adapt the rendering pipeline in order to integrate the OST-HMD calibration framework. An evaluation with a user-perspective camera shows that the system achieves mean temporal error of <;1 ms (95% reduction of the latency from naive, no-predictive rendering), and median spatial error <;0.3° in the viewing angle with maximum error at most 1.0°.

We propose a method to calibrate viewpoint-dependent, channel-wise image blur of near-eye displays, especially of Optical See-Through Head-Mounted Displays (OST-HMDs). Imperfections in HMD optics cause channel-wise image shift and blur that degrade the image quality of the display at a user's viewpoint. If we can estimate such characteristics perfectly, we could mitigate the effect by applying correction techniques from the computational photography in computer vision as analogous to cameras. Unfortunately, directly applying existing calibration techniques of cameras to OST-HMDs is not a straightforward task. Unlike ordinary imaging systems, image blur in OST-HMDs is viewpoint-dependent, i.e., the optical characteristic of a display dynamically changes depending on the current viewpoint of the user. This constraint makes the problem challenging since we must measure image blur of an HMD, ideally, over the entire 3D eyebox in which a user can see an image. To overcome this problem, we model the viewpoint-dependent blur as a Gaussian Light Field (GLF) that stores spatial information of the display screen as a (4D) light field with depth information and the blur as point-spread functions in the form of Gaussian kernels, respectively. We first describe both our GLF model and a calibration procedure to learn a GLF for a given OST-HMD. We then apply our calibration method to two HMDs that use different optics: a cubic prism or holographic gratings. The results show that our method achieves significantly better accuracy in Point-Spread Function (PSF) estimations with an accuracy about 2 to 7 dB in Peak SNR.

In order to produce realistic simulations and enhance immersion in augmented reality systems, solutions must not only present a realistic visual rendering of virtual objects, but also allow natural hand interactions. Most approaches capable of understanding user interaction with virtual content can often be restrictive or computationally expensive. To cope with these problems, we demonstrate a method which employs user's thumb and forefinger to interact with the virtual content in a natural way, utilizing a single RGB-D camera. Based on this method, we develop and realise an augmented reality chess game, focused on providing an immersive experience to users, so that they are able to manipulate virtual chess pieces seamlessly over a board of markers and play against a chess engine.

In Augmented Reality (AR) with an Optical See-Through Head-Mounted Display (OST-HMD), the spatial calibration between a user's eye and the display screen is a crucial issue in realizing seamless AR experiences. A successful calibration hinges upon proper modeling of the display system which is conceptually broken down into an eye part and an HMD part. This paper breaks the HMD part down even further to investigate optical aberration issues. The display optics causes two different optical aberrations that degrade the calibration quality: the distortion of incoming light from the physical world, and that of light from the image source of the HMD. While methods exist for correcting either of the two distortions independently, there is, to our knowledge, no method which corrects for both simultaneously. This paper proposes a calibration method that corrects both of the two distortions simultaneously for an arbitrary eye position given an OST-HMD system. We expand a light-field (LF) correction approach [8] originally designed for the former distortion. Our method is camera-based and has an offline learning and an online correction step. We verify our method in exemplary calibrations of two different OST-HMDs: a professional and a consumer OST-HMD. The results show that our method significantly improves the calibration quality compared to a conventional method with the accuracy comparable to 20/50 visual acuity. The results also indicate that only by correcting both the distortions simultaneously can improve the quality.

The current advent of consumer level optical see-through (OST) head-mounted displays (HMD's) has greatly broadened the accessibility of Augmented Reality (AR) to not only researchers but also the general public as well. This increased user base heightens the need for robust automatic calibration mechanisms suited for nontechnical users. We are developing a fully automated calibration system for two stereo OST HMD's, a consumer level and prototype model, based on the recently introduced interaction free display calibration (INDICA) method. Our current efforts are also focused on the development of an evaluation process to assess the performance of the system during use by non-expert subjects.

The fundamental issues in Augmented Reality (AR) are on how to naturally mediate the reality with virtual content as seen by users. In AR applications with Optical See-Through Head-Mounted Displays (OST-HMD), the issues often raise the problem of rendering color on the OST-HMD consistently to input colors. However, due to various display constraints and eye properties, it is still a challenging task to indistinguishably reproduce the colors on OST-HMDs. An approach to solve this problem is to pre-process the input color so that a user perceives the output color on the display to be the same as the input. We propose a color calibration method for OST-HMDs. We start from modeling the physical optics in the rendering and perception process between the HMD and the eye. We treat the color distortion as a semi-parametric model which separates the non-linear color distortion and the linear color shift. We demonstrate that calibrated images regain their original appearance on two OST-HMD setups with both synthetic and real datasets. Furthermore, we analyze the limitations of the proposed method and remaining problems of the color reproduction in OST-HMDs. We then discuss how to realize more practical color reproduction methods for future HMD-eye system.

A critical requirement for AR applications with Optical See-Through Head-Mounted Displays (OST-HMD) is to project 3D information correctly into the current viewpoint of the user - more particularly, according to the user's eye position. Recently-proposed interaction-free calibration methods [16], [17] automatically estimate this projection by tracking the user's eye position, thereby freeing users from tedious manual calibrations. However, the method is still prone to contain systematic calibration errors. Such errors stem from eye-/HMD-related factors and are not represented in the conventional eye-HMD model used for HMD calibration. This paper investigates one of these factors - the fact that optical elements of OST-HMDs distort incoming world-light rays before they reach the eye, just as corrective glasses do. Any OST-HMD requires an optical element to display a virtual screen. Each such optical element has different distortions. Since users see a distorted world through the element, ignoring this distortion degenerates the projection quality. We propose a light-field correction method, based on a machine learning technique, which compensates the world-scene distortion caused by OST-HMD optics. We demonstrate that our method reduces the systematic error and significantly increases the calibration accuracy of the interaction-free calibration.

With the growing availability of optical see-through (OST) head-mounted displays (HMDs) there is a present need for robust, uncomplicated, and automatic calibration methods suited for non-expert users. This work presents the results of a user study which both objectively and subjectively examines registration accuracy produced by three OST HMD calibration methods: (1) SPAAM, (2) Degraded SPAAM, and (3) Recycled INDICA, a recently developed semi-automatic calibration method. Accuracy metrics used for evaluation include subject provided quality values and error between perceived and absolute registration coordinates. Our results show all three calibration methods produce very accurate registration in the horizontal direction but caused subjects to perceive the distance of virtual objects to be closer than intended. Surprisingly, the semi-automatic calibration method produced more accurate registration vertically and in perceived object distance overall. User assessed quality values were also the highest for Recycled INDICA, particularly when objects were shown at distance. The results of this study confirm that Recycled INDICA is capable of producing equal or superior on-screen registration compared to common OST HMD calibration methods. We also identify a potential hazard in using reprojection error as a quantitative analysis technique to predict registration accuracy. We conclude with discussing the further need for examining INDICA calibration in binocular HMD systems, and the present possibility for creation of a closed-loop continuous calibration method for OST Augmented Reality.

In recent years optical see-through head-mounted displays (OST-HMDs) have moved from conceptual research to a market of mass-produced devices with new models and applications being released continuously. It remains challenging to deploy augmented reality (AR) applications that require consistent spatial visualization. Examples include maintenance, training and medical tasks, as the view of the attached scene camera is shifted from the user's view. A calibration step can compute the relationship between the HMD-screen and the user's eye to align the digital content. However, this alignment is only viable as long as the display does not move, an assumption that rarely holds for an extended period of time. As a consequence, continuous recalibration is necessary. Manual calibration methods are tedious and rarely support practical applications. Existing automated methods do not account for user-specific parameters and are error prone. We propose the combination of a pre-calibrated display with a per-frame estimation of the user's cornea position to estimate the individual eye center and continuously recalibrate the system. With this, we also obtain the gaze direction, which allows for instantaneous uncalibrated eye gaze tracking, without the need for additional hardware and complex illumination. Contrary to existing methods, we use simple image processing and do not rely on iris tracking, which is typically noisy and can be ambiguous. Evaluation with simulated and real data shows that our approach achieves a more accurate and stable eye pose estimation, which results in an improved and practical calibration with a largely improved distribution of projection error.

An issue in AR applications with Optical See-Through Head-Mounted Display (OST-HMD) is to correctly project 3D information to the current viewpoint of the user. Manual calibration methods give the projection as a black box which explains observed 2D-3D relationships well (Fig. 1). Recently, we have proposed an INteraction-free DIsplay CAlibration method (INDICA) for OST-HMD, utilizing camera-based eye tracking [7]. It reformulates the projection in two ways: a black box with an actual eye model (Recycle Setup), and a combination of an explicit display model and an eye model (Full Setup). Although we have shown the former performs more stably than a repeated SPAAM calibration, we could not yet prove whether the same holds for the Full Setup. More importantly, it is still unclear how the error in the calibration parameters affects the final results. Thus, the users can not know how accurately they need to estimate each parameter in practice. We provide: (1) the fact that the Full Setup performs as accurately as the Recycle Setup under a marker-based display calibration, (2) an error sensitivity analysis for both SPAAM and INDICA over the on-/offline parameters, and (3) an investigation of the theoretical sensitivity on an OST-HMD justified by the real measurements.

A correct spatial registration of Optical See-Through Head-Mounted Displays (OST-HMD) w.r.t. a user's eye(s) is an essential problem for any AR application using the such HMDs (Fig. 1). Maintaining the correct registration demands frequent (re)calibrations for the end-users whenever they move the HMD on their head. Thus, a calibration technique should be simple and accurate for the universal, long-run use of the displays. This demonstration showcases INDICA, an automatic OST-HMD calibration approach presented in our previous work[1] and ISMAR 2014 paper [2]. The method calibrates the display to the user's current eyeball position by combining online eye-position tracking with offline parameters. Visitors of our demonstration can try our both manual calibration and our interaction-free calibration on a customized OST-HMD.