实时立体视觉系统中的深度映射

目的 为减少立体图像中由于水平视差过大引起的视觉疲劳。针对实时渲染的立体视觉系统,给出了一种非均匀深度压缩方法。方法 该方法在单一相机空间内,通过不同的投影变换矩阵生成双眼图像,水平视差由投影变换来控制。为减少深度压缩造成的模型变形而带来的瑕疵,将不同深度区域内物体施以不同的压缩比例;将相机轴距表示为深度的连续函数,通过相机轴距推导出在单一相机空间内获取双眼图像的坐标变换,将深度压缩转换为模型的坐标变换,从而保证压缩比例的连续变化。结果 实验结果表明,该方法能有效提高立体图像的质量。结论 该方法简单、高效,可应用于游戏、虚拟现实等实时立体视觉系统。     

Perceived enablers of 3D virtual environments for virtual team learning and innovation

Virtual teams consist of geographically distributed employees working with a common goal using mostly technology for communication and collaboration. Virtual teams face a number of challenges, discussed in the literature in terms of communication through technology, difficulty in building trust, conveying social cues, and creating awareness, as well as cultural differences. These challenges impact collaboration, but also learning and innovation. This research focuses on how a social medium, the 3D virtual environment, is perceived to enable learning and innovation in virtual teams. We study this through a qualitative study based on interviews of distributed work managers’ perception of VEs. The major findings are that VEs are perceived to create collaborative learning atmospheres for virtual teams in terms of enabling engagement, a shared context awareness, and support in social network building. Another finding is that VEs are perceived to enable team learning, knowledge development, and collaboration through persistence of content, information sharing, learning through role-plays and simulations, and visualization. Furthermore, VEs enable the development of co-created content as well as new ways of working in virtual teams.     

Spatial judgments with monoscopic and stereoscopic presentation of perspective displays.

Spatial judgments with monoscopic and stereoscopic presentation of perspective displays were investigated in the present study. The stimulus configuration emulated a visual scene consisting of a volume of airspace above a ground reference plane. Two target symbols were situated at various positions in the space, and observers were instructed to identify the relative depth or altitude of the two symbols. Three viewing orientations (15, 45, or 90 deg elevation angle) were implemented in the perspective projection. In the monoscopic view, depth cues in size, brightness, occlusion, and linear perspective were provided in the format. In the stereoscopic view, binocular disparity was added along the line of sight from the center of projection to reinforce the relative depth in the visual scene. Results revealed that spatial judgments were affected by manipulation of the relative spatial positions of the two target symbols and by the interaction between relative position and viewing orientation. The addition of binocular disparity improved judgments of three-dimensional spatial relationships, and the enhancement was greater when monocular depth cues were less effective and/or ambiguous in recovering the three-dimensional spatial characteristics.     

Impact of parallax and interpupillary distance on size judgment performances of virtual objects in stereoscopic displays

Effective interactions in both real and stereoscopic environments require accurate perceptions of size and position. This study investigated the effects of parallax and interpupillary distance (IPD) on size perception of virtual objects in widescreen stereoscopic environments. Twelve participants viewed virtual spherical targets displayed at seven different depth positions, based on seven parallax levels. A perceptual matching task using five circular plates of different sizes was used to report the size judgment. The results indicated that the virtual objects were perceived as larger and smaller than the corresponding theoretical sizes, respectively, in negative and positive parallaxes. Similarly, the estimates from participants with small IPDs were greater than the predicted estimates. The findings of this study are used to explain human factor issues such as the phenomenon of inaccurate depth judgments in virtual environments, where compression is widely reported, especially at farther egocentric distances. Furthermore, a multiple regression model was developed to describe how the size was affected by parallax and IPD.

Practitioner Summary: The study investigates the effects of parallax and interpupillary distance on size perception of virtual targets in a stereoscopic environment. Virtual objects were perceived as larger in negative and smaller in positive parallax. Also, size estimates were greater than the theoretical sizes for participants with smaller IPD. A multiple-regression model explains the impact of parallax and measured IPD. Abbreviations IPD interpupillary distance

VR virtual eality

HMD head mounted-displays

2AFC two-alternative forced choice

IOD interocular distance

PD pupillary distance

ANOVA analysis of variance

     

Transformations for stereoscopic visual simulation

Stereoscopic display devices are now standard offerings for graphics workstations. These displays find application in medical, scientific, and engineering visualization. Several geometric models can be used to determine the projections for stereoscopic images. In some circumstances, however, the perceived image may be uncomfortable to view, or it may contain undesirable depth distortions. We present a geometric model for stereoscopic viewing that can accurately model most viewing situations. Using this model, the viewer comfortably perceives realistic size and depth relationships among objects in the stereoscopic image. We relate this model to human visual constraints, and develop the geometric transformations required to use this method on graphics workstations.     

Depth perception for moving images shown on a large LED display with an aperture grille

Abstract— A type of depth illusion created by the use of an aperture grille is reported. When viewing a moving target through multiple slits, a movement with depth is perceived, which was originally reported (see Ref. 11). The binocular delay is considered to cause a virtual disparity between both perspective images with apparent movement. By using an LED display with an aperture grille as a stereoscopic display, perceived distance caused by a binocular delay has been measured. The measured distance is compared with the perceived distance for stereoscopic still images shown on a stereoscopic LED panel. The comparison supported that the binocular delay is converted into binocular disparity. Furthermore, pair‐comparison tests were conducted to investigate depth impressions. It was found that use of an aperture grille improves depth impression for a movie that was taken with a laterally moving camera.     

See-through techniques for referential awareness in collaborative virtual reality

Multi-user virtual reality systems enable natural collaboration in shared virtual worlds. Users can talk to each other, gesture and point into the virtual scenery as if it were real. As in reality, referring to objects by pointing results often in a situation whereon objects are occluded from the other users' viewpoints. While in reality this problem can only be solved by adapting the viewing position, specialized individual views of the shared virtual scene enable various other solutions. As one such solution we propose show-through techniques to make sure that the objects one is pointing to can always be seen by others. We first study the impact of such augmented viewing techniques on the spatial understanding of the scene, the rapidity of mutual information exchange as well as the proxemic behavior of users. To this end we conducted a user study in a co-located stereoscopic multi-user setup. Our study revealed advantages for show-through techniques in terms of comfort, user acceptance and compliance to social protocols while spatial understanding and mutual information exchange is retained. Motivated by these results we further analyze whether show-through techniques may also be beneficial in distributed virtual environments. We investigated a distributed setup for two users, each participant having its own display screen and a minimalist avatar representation for each participant. In such a configuration there is a lack of mutual awareness, which hinders the understanding of each other's pointing gestures and decreases the relevance of social protocols in terms of proxemic behavior. Nevertheless, we found that show-through techniques can improve collaborative interaction tasks even in such situations.     

The co-learning process in healthcare professionals: Assessing user satisfaction in virtual communities of practice

Communities of practice are nowadays an important concept in the healthcare sector. Particularly, the intensive use of ICT has allowed their creation into a virtual environment – Virtual Communities of Practice (VCoPs) developing optimal conditions to make possible the collaborative learning process. The VCoPs antecedents can be situated on social network phenomenon, where individuals with different traits but a common interest/objective are linked, use ICT potency (especially social media) to interchange information, experiences and contents among them. And as a result, people create and share knowledge, and learn collaboratively. VCoP users have a higher satisfaction level in the collaborative learning process when they can: (1) Achieve benefits related to patient diagnosis and treatment (cost reductions, faster management, quality and accuracy of diagnosis, etc.); (2) Increase the share capital of participants and creating networks of trusted individuals. Given the interest in this topic, the objective of this work is to identify the factors that determine user satisfaction in relation to Community Practice (CoP) and the process of building shared knowledge. For this, a sample of 130 Spanish health professionals participating in an online community, and developed in a virtual community of practice, is discussed. The results obtained from an analysis of logistic regression show evidence of the perception of efficiency and effectiveness in collaboration with the members of the VCoP as positively influencing the perceived satisfaction with the CoP. Also, the degree of individual participation in the community affects the degree of perceived satisfaction. The conclusions provide interesting strategic recommendations in the management process of the CoP.     

Virtual toed‐in camera method to eliminate parallax distortions of stereoscopic images for stereoscopic displays

Abstract— The parallax images captured by a toed‐in camera have positive and negative horizontal parallax for stereoscopic displays, but they also have parallax distortions including horizontal and vertical distortions. The virtual toed‐in camera method can eliminate the horizontal distortion and reduce the vertical distortion. The parallax formulae for the corrected‐parallax images were deduced. The experiments were carried out and the results proved that the method was accurate. Good stereoscopic images without horizontal distortion and with little vertical distortion were presented on an autostereoscopic display.     

Tuning self-motion perception in virtual reality with visual illusions

Motion perception in immersive virtual environments significantly differs from the real world. For example, previous work has shown that users tend to underestimate travel distances in virtual environments (VEs). As a solution to this problem, researchers proposed to scale the mapped virtual camera motion relative to the tracked real-world movement of a user until real and virtual motion are perceived as equal, i.e., real-world movements could be mapped with a larger gain to the VE in order to compensate for the underestimation. However, introducing discrepancies between real and virtual motion can become a problem, in particular, due to misalignments of both worlds and distorted space cognition. In this paper, we describe a different approach that introduces apparent self-motion illusions by manipulating optic flow fields during movements in VEs. These manipulations can affect self-motion perception in VEs, but omit a quantitative discrepancy between real and virtual motions. In particular, we consider to which regions of the virtual view these apparent self-motion illusions can be applied, i.e., the ground plane or peripheral vision. Therefore, we introduce four illusions and show in experiments that optic flow manipulation can significantly affect users' self-motion judgments. Furthermore, we show that with such manipulations of optic flow fields the underestimation of travel distances can be compensated.     

Immersive Whiteboard Collaborative System

An immersive whiteboard system is presented where users at multiple locations can communicate with each other. The system features a virtual environment with vivid avatars, stroke compression and streaming technology to effectively deliver stroke data across meeting participants, friendly human interaction and navigation, virtual and physical whiteboard. The whiteboard is both a physical platform for our input/output interfaces and a virtual screen for sharing common multimedia. It is this whiteboard correspondence that allows the user to physically write on the virtual whiteboard. In addition to drawing on the shared virtual board, the immersive whiteboard in our setup permits users to control the application menus, insert multimedia objects into the world, and navigate around the virtual environment. By integrating multimedia objects and avatar representations into an immersive environment, we provide the users with a more transparent medium so that they feel as if they are communicating and interacting face-to-face. The whiteboard efficiently pulls all the collaboration technologies together. The goal of this collaborative system is to provide a convenient environment for participants to interact with each other and support collaborative applications such as instant messaging, distance learning and conferencing.     

Hairy Slices II: Depth Cues for Visualizing 3D Streamlines Through Cutting Planes

Visualizing 3D vector fields is challenging because of occlusion problems and the difficulty of providing depth cues that adequately support the perception of direction of flow lines in 3D space. One of the depth cues that has proven most valuable for the perception of other kinds of 3D data, notably 3D networks and 3D point clouds, is structure-from-motion (also called the Kinetic Depth Effect); another powerful depth cue is stereoscopic viewing. We carried out an experiment of the perception of direction for short streamlines passing through a cutting plane. The conditions included viewing with and without structure-from-motion and with and without stereoscopic depth. Conditions also include comparing streamtubes to lines. The results show that for this particular task, stereo provided an effective depth cue, but structure-from-motion did not. Ringed streamtubes and streamcones provided good 3D direction information, even without stereoscopic viewing. We conclude with guidelines for viewing slices through vector fields.     

Measurement of the lens accommodation in viewing stereoscopic displays

In observing the stereoscopic display at the viewing distance of 1 m, the amount of the perceived depth was determined by the positions of the crossing point that the viewing direction of two eyes intersect. The positions of the crossing points of stereoscopic stimuli were controlled, and the accommodation was measured by the autorefractometer for the seven participants. Accommodation was also measured when viewing the real film chart which was placed at the same position as these crossing points. The accommodation change when viewing the stereoscopic display was measured to be noticeable only when the crossing point was quite near the participant, but this change was still much smaller compared with the accommodation change when viewing the real film chart. This change in accommodation implies the possible occurrence of fatigue related to the accommodation–convergence conflict, while the constant accommodation within the range of DOF implies no conflict between the accommodation and convergence. This measurement scheme may be used to define the range of DOF where the accommodation remains little changed, and thus define the depth of the 3D object at which no accommodation–convergence conflict occurs, for a given stereoscopic display.     

The effects of cast shadows and stereopsis on performing computer-generated spatial tasks

More powerful computer hardware and software has enabled the development of numerous depth-cue techniques to depict the three-dimensional (3D) characteristics of computer-generated imagery. Particularly, the role of stereoscopic viewing in promoting the depth perception of objects in 3D space has been widely studied. However, there has been little study of the use of cast shadows in this context, and few investigations of how computer-generated depth cues are perceptually integrated. To investigate these issues, subjects: 1) position a sphere to complete a directional vector/vector segment extending in space and 2) resize a sphere to match the perceived size of a second sphere displaced in space. Task accuracies and response times are recorded under the following conditions: 1) stereoscopic, and monoscopic, scene viewing; 2) objects casting zero, or one shadow; 3) flat, and zig-zag, background surface shapes; and 4) solid and checkerboard background surface textures. The results suggest that, of the cues considered, stereo viewing has a consistently beneficial effect on positioning and resizing spheres in depth. However, objects casting shadows improve positioning accuracy to a level afforded by stereo viewing. Finally, more complex scene backgrounds impair positioning and resizing task performances. Implications for the design of effective 3D user interfaces are discussed.     

Distortion conspicuity on stereoscopically viewed 3D images may correlate to scene content and distortion type

We describe two studies that were aimed towards increasing our understanding of how the visibility of distortions on stereoscopically viewed 3D images is affected by scene content and distortion types. By assuming that subjects' performance would be highly correlated with the visibility of local distorted patches, we analyzed subjects' performance in locating distortion patches when viewing stereoscopic 3D images. Subjects' performances are measured by whether they successfully locate a local distorted patch, the times they spent to finish the task, and subjective quality ratings given by subjects. The visual data used in this work are co‐registered stereo images with co‐registered “ground truth” range (depth) data. Varied statistical analysis methods were used to discuss the significance of our observations. Three observations are drawn from our analyses. First, blur, JPEG, and JP2K distortions in stereo 3D images may be suppressed if one of the left or right views is undistorted. Second, contrast masking ^a does not occur, or is reduced, while viewing white noise distorted stereo 3D images. Third, there is no depth/disparity masking effect when viewing stereo 3D images, but there may be (conversely) depth‐related facilitation ^b effects for blur, JPEG, and JP2K distorted stereo 3D images.     

The accuracy of distance perception in the frontal plane of projection‐based stereoscopic environments

An experiment was conducted to investigate the accuracy of distance judgment in a frontal plane of projection‐based stereoscopic environments. The targets were presented at nine distinct frontal plane positions and at three depth levels. Eighteen right‐handed participants with self‐declared normal visual acuity reached the target, either continuously visible or presented briefly, by holding pointing sticks. All combinations of the experimental conditions were repeated for an equivalent real‐world environment. Accuracies of judgments were then computed from three‐dimensional data collected by a motion system composed of six infrared cameras. As compared with about 94% accuracy in the physical world, the space in the frontal plane was only about 85% on the stereoscopic environment. The result also revealed more accurate judgment in the continuous presence of the target. Furthermore, the accuracy was affected by the egocentric distance of the frontal plane from the position of the participant. The study concluded that the compression in the frontal plane and underestimation of depth, which has been reported by the majority of previous studies could be an indication that the space compression in virtual environments might be in all the three‐dimensions. These findings can be used as guidelines for developers and content designers to properly locate virtual targets and selection of efficient interaction modes.     

On adjustment of stereo parameters in multiview synthesis for planar 3D displays

This paper investigates the impacts of stereo parameters in multiview synthesis for planar 3D display and presents a novel parameter adjustment method for reducing visual discomforts and geometric distortions. The proposed method combines the geometry of stereoscopic capturing system with the comfortable viewing rules for the human vision system in three steps. First, an identically sized representation between the virtual space and the display space is established, and the virtual camera parameters are derived based on the stereo geometry. Second, the scale factor between the physical space and the virtual space is computed based on the depth of focus theory to diminish vergence–accommodation conflicts. Last, the capturing and displaying parameters are adjusted according to the comfortable viewing zone and personal preference. Experimental results demonstrated that a reliable basis for multiview image synthesis and a more comfortable stereo perception can be achieved by applying the proposed method.     

A technique for precise depth representation in stereoscopic display

In observing a virtual 3D object displayed stereoscopically on a large screen, there is often a difference between the calculated depth and the perceived depth. This paper presents a method for reducing such differences of depth. To do this, we modify both the viewing position and the screen position in the stereoscopic calculation. The optimal amount of modification was determined from sample values of depth differences. The effectiveness of the proposed method is discussed on the merits of the experimental results. This technique decreased the average difference from 4.3 mm to 1.3 mm.     

Stereo Viewing and Virtual Reality Technologies in Mobile Robot Teleguide

The use of 3-D stereoscopic visualization may provide a user with higher comprehension of remote environments in teleoperation when compared with 2-D viewing, in particular, a higher perception of environment depth characteristics, spatial localization, remote ambient layout, faster system learning, and decision performance. Works in the paper have demonstrated how stereo vision contributes to the improvement of the perception of some depth cues, often for abstract tasks, while it is hard to find works addressing stereoscopic visualization in mobile robot teleguide applications. This paper intends to contribute to this aspect by investigating the stereoscopic robot teleguide under different conditions, including typical navigation scenarios and the use of synthetic and real images. This paper also investigates how user performance may vary when employing different display technologies. Results from a set of test trials run on seven virtual reality systems, from laptop to large panorama and from head-mounted display to Cave automatic virtual environment (CAVE), emphasized few aspects that represent a base for further investigations as well as a guide when designing specific systems for telepresence.      

Optical compensation for two stereoscopic distortions

Abstract— A stereoscopic display configuration for presenting stereoscopic images without keystone and depth‐plane‐curvature distortions is proposed. The main idea of the proposed configuration is to perform optical compensation for these distortions by presenting left and right perspective images at two intersecting screens. The possibility of such distortion elimination was proven by two independent ways: analytically and graphically.