Generation of images for a time-multiplexed stereoscopic display environment is not a straightforward extension of image generation in a perspective graphics environment. There are several factors that must be taken into account in order to produce high-quality, stereographic images. An overview is provided of some of the factors that are important to the proper construction and display of computer graphic images in a time-multiplexed environment. In particular, image generation algorithms, horizontal parallax, interocular cross talk and ghosting, refresh rate, image scaling, and interaction with 3-D spaces are discussed.

An interactive stereo system was implemented to allow a user to draw and modify B-Spline space curves. A time-multiplexed, liquid crystal shutter system was used to produce true three-dimensional output. A six degree-of-freedom input device was used to drive and control the stereoscopic cursor. Several different cursor types were investigated to determine which were suited to this application. Cursor characteristics were examined to determine their influence on the user''s ability to accurately and proficiently use the system.

Surface reconstruction is an important problem within computer vision. This paper studies the application of the Lagrange polynomials to interpolating three-dimensional stereo data. The process consists of fitting a surface function to the given 3-D data. The value of the constructed surface at a point (x,y) is calculated locally in finite intervals based on the data at relatively nearby points. This produces a large number of polynomials; however, it requires less computational time than a global solution. This local interpolation is of interest when considering unusual shapes where the data points are irregularly scattered throughout the 3-D space. Overlapping is used when constructing the polynomials to ensure the continuity and smoothness of the surfaces from one scene point to the next. Because the data are generally sparse, the horizontal and vertical one-dimensional operations give different results. Final approximation is based on minimizing the error based on the least square criterion. Experiments show that the method produces good results.

A method for simultaneous generation of stereoscopic images of implicitly defined surfaces is presented. Ray tracing, a computationally intensive but `photo-realistic'' rendering technique, is used to generate these images. Traditional ray tracing of stereoscopic images involves generating left eye and right eye images separately, which effectively doubles the computational work involved. A method originally developed for animation and later adopted for stereo ray tracing achieves computational speedup in ray tracing stereoscopic images by generating the right eye image as the left eye image is generated. The work presented here extends that method to obtain stereoscopic images of implicitly defined surfaces of the form f(x,y,z) equals 0. Implicitly defined quadric surfaces such as spheres, ellipsoids, hyperboloids of one sheet and two sheets, and surfaces derived from fault-tolerant software modeling applications were rendered using this method. The speedups achieved for these surfaces under different stereoscopic setups are compared and tabulated.

A sequence of steps to produce synthetic stereo scenes from hardcopy aerial photographs is discussed. First, a digital terrain model (DTM) is collected from existing stereo coverage by conventional photogrammetric techniques. One photograph of the pair is converted into digital form by scanning, including the fiducial or registration marks. Its position and orientation parameters are retained from the original stereo setup. The images of a synthetic stereo pair are constructed by selecting two fictitious photo stations and orientations (with reasonable base-height ratio). The three-dimensional terrain model is projected onto the fictitious photo planes and the facets `draped'' with corresponding image densities from the original scanned image. Such stereo pairs can be viewed using a split-image/stereoscope setup on a standard PC display, or on a high-resolution display using frame-sequential format and liquid crystal stereo shutter.

With recent advances in 3-D technology, computer users have the opportunity to work within a natural 3-D environment; a flat panel LCD computer display of this type, the DTI-100M made by Dimension Technologies, Inc., recently went on the market. In a joint venture between DTI and NCSU, an object-oriented 3-D drawing application, 3-D Draw, was developed to address some issues of human interface design for interactive stereo drawing applications. The focus of this paper is to determine some of the procedures a user would naturally expect to follow while working within a true 3-D environment. The paper discusses (1) the interface between the Macintosh II and DTI-100M during implementation of 3-D Draw, including stereo cursor development and presentation of current 2-D systems, with an additional `depth'' parameter, in the 3-D world, (2) problems in general for human interface into the 3-D environment, and (3) necessary functions and/or problems in developing future stereoscopic 3-D operating systems/tools.

Many stereovision algorithms are based on the assumption that the images are registered in epipolar geometry. This requires that the two cameras of a vision system are aligned such that the camera axes are parallel and also perpendicular to the camera base. Initially, the cameras of a moving robot may be perfectly aligned, but this condition is likely to change in time. It is argued that the camera positions should be periodically surveyed and, if necessary, readjusted. The camera positions can be determined by an automatic orientation. In this paper, a method to compute the epipolar geometry from known camera positions is described. After defining the problem, the authors derive algorithms to resample the original images such that they satisfy the condition of epipolar geometry.

An overview on the state of the art of 3-DTV in Europe is given, and the new European Co- operation in the Field of Scientific and Technical Research (COST) project and its objectives are described. The paper starts with a report on 3-DTV broadcast transmissions in 1982 using the simple anaglyph technique, which in many European countries found enthusiastic public interest. Following that, in three international audio and video fairs in 1983, 1985, and 1987 in Berlin, presentations of a high-quality two-channel 3-DTV system using large screen projection, showing professionally produced demonstration programs, attracted about 50,000 visitors. Meanwhile, several 3-DTV activities for advertising, information, and special applications such as medical imaging are to be found. In the broadcast domain, research and development aim to transmit 3-DTV within a high-definition TV channel.

Two experiments were performed to rank different types of display formats common to CAD applications in terms of geometric information conveyed and perceived realism of objects. Display types tested were: wireframe, wireframe with hidden lines removed (HLR), shaded solid, orthogonal multiview, stereoscopic wireframe, stereoscopic HLR, and stereoscopic shaded solid. The results of the geometric information experiment indicated that the orthogonal multiview display was judged inferior to both the nonstereo and stereo pictorial displays and that the stereo displays were judged superior to the nonstereo displays in providing geometric information to the subject. Individual preferences among subjects, however, varied widely. The results of the realism experiment indicated that the flat shaded stereo, HLR stereo, and the flat shaded display types were judged to be equivalent and most realistic. The wireframe stereo, HLR, and wireframe displays were judged to be equivalent and less realistic. The orthogonal views display was judged to be the least realistic.

`Pathway-in-the-sky'' flight display formats appear to offer exceptional path-control precision for future transport operational environments requiring complex-path approaches. With the conversion from the present instrument landing system (ILS) to the microwave landing system (MLS) within the National Airspace System, complex-path approaches could be used for commercial transport operations to address airport capacity issues. Therefore, the application of `pathway-in-the-sky'' formats to commercial transport operations is being evaluated at various flight display research laboratories. The introduction of true depth cues via stereopsis techniques offers a means of further enhancing these displays. The paper describes research conducted to determine the effectiveness of two candidate pathway formats for landing approach and to investigate the effect of their presentation in stereo versus nonstereo display environments. A real-time piloted simulation experiment comparing performance across these factors in a transport landing-approach task is discussed.

Within the limited research literature on the topic, there is considerable controversy over the usefulness of stereoscopic TV displays for performing remote manipulation tasks. Some investigators argue that a second video channel might just as well be allocated to a camera with an appropriately separated view of the worksite -- an `orthogonal'' view to that of the first camera. Other researchers argue that even though operators tend to express strong subjective preferences for stereoscopic displays, these displays often do not provide objective performance advantages. In this experiment, a group of relatively inexperienced manipulator operators performed a complex and difficult line threading task remotely and varied the visual displays available to the operators while performing this task. For each video display condition tested, the operator sat in a centered position facing two CRTs, each providing a separate view of the remote task site. Three combinations of video display types were tested: (1) monoscopic view plus orthogonal view, (2) stereoscopic view plus orthogonal view, and (3) stereoscopic view plus monoscopic view. Total task completion times, manipulative errors, and operator gaze references were measured for each combination of display types. Results show a strong and consistent operator viewing preference for stereoscopic displays as well as substantial and statistically significant performance advantages for those display combinations that provided a stereoscopic view over those that provided only monoscopic views.

The virtual window display is a hybrid of the head-coupled, helmet-mounted display and the fixed CRT mounted on a tabletop. Moving the CRTs from the operator''s head retains the benefits of motion parallax while providing higher quality color images, greater comfort and fewer restrictions on the operator''s view of the control site. A prototype virtual window display was constructed with direct mechanical linkage to servo camera movements to the operator''s head motions. This apparatus was used to compare remote performance with and without motion parallax, paired with either stereoscopic or monoscopic views. Mean stereoacuity and depth scaling responses for six observers of a Howard-Dolman apparatus showed improved performance when motion parallax accompanied monoscopic, but not stereoscopic view. Mean performance times for six observers retrieving objects from a wire maze show similar, though not significant, improvement when motion parallax accompanies monoscopic view. Observers report that manipulator requirements for hand steadiness reduce the opportunity to get depth information from head movements. The use of motion parallax information in a monoscopic virtual window display can improve teleoperator performance.

Formal studies to date do not allow system developers to answer the question: is stereo video necessary for remote driving in the operational, off-road environment? This paper proposes a study consisting of two experiments: (1) a high-speed maneuvering test and (2) a visual planning test. The high-speed maneuvering test has been designed to evaluate the possible performance benefits of stereo in uncluttered off-road environments. The visual planning experiment has been designed to measure the operator''s capability to analyze a scene to determine the placement of hazard(s). Course designs as well as experimental protocols for the proposed tests are presented.

This study explores the research hypothesis that perceptual learning could occur with visual exposure to a repeating alternation between 2-D vs 3-D video images of terrain hazards typically encountered in off-road driving of ground vehicles. In individual sessions, each of the nine untrained test subjects was shown 20 off-road terrain-hazard scenes on a color video display. Each hazard was shown first in 2-D mode, then in 3-D mode, and then with 2-D/3-D mode alternating on the video screen. In 2-D mode, only one of the 20 terrain hazards was perceived by two of the nine subjects, whereas all 20 terrain hazards were immediately perceived by all subjects when the display switched over to 3-D mode. A post-test presented mirror-image versions of the same 20 hazards in 2-D only, to determine if the previous 2-D/3- D alternation treatment improved the ability to detect terrain hazards in 2-D mode. At the end of their session, test subjects were given a questionnaire asking them to rate the degree of perceptual training resulting from 2-D/3-D alternation. All 20 subjects reported that the 2-D/3- D alternation improved their sensitivity to the monocular cues of terrain hazards presented on a 2-D video display. The implications that can be drawn from this preliminary study are: (1) in off-road driving by means of a conventional 2-D video display, operators will fail to perceive many significant terrain hazards; (2) however, with a 3-D video display, operators will immediately perceive most terrain hazards and will interpret terrain contours easily and accurately; (3) a more extensive experiment is indicated to formally determine the extent of the perceptual training that can be obtained by 2-D/3-D alternation.

For stereoscopic photography or telepresence, orthostereoscopy occurs when the perceived size, shape, and relative position of objects in the three-dimensional scene being viewed match those of the physical objects in front of the camera. In virtual reality, the simulated scene has no physical counterpart, so orthostereoscopy must be defined in this case as constancy, as the head moves around, of the perceived size, shape, and relative positions of the simulated objects. Achieving this constancy requires that the computational model used to generate the graphics match the physical geometry of the head-mounted display being used. This geometry includes the optics used to image the displays and the placement of the displays with respect to the eyes. The model may fail to match the geometry because model parameters are difficult to measure accurately, or because the model itself is in error. Two common modeling errors are ignoring the distortion caused by the optics and ignoring the variation in interpupillary distance across different users. A computational model for the geometry of a head-mounted display is presented, and the parameters of this model for the VPL EyePhone are calculated.

A recently completed implementation of a virtual environment for the analysis of three- dimensional steady flowfields is described. The hardware consists of a boom-mounted, six- degree-of-freedom head position sensitive stereo CRT system for display, a glove controller for placement of tracer particles within the flow, and a high-performance 3-D graphics workstation for computation and rendering. The flowfields that are visualized using the virtual environment are velocity vector fields defined on curvilinear meshes, and are the steady-state solutions to problems in computational fluid dynamics. The system is applicable to the visualization of other vector fields as well.

Along with the marriage of motion pictures and computers has come an increasing interest in making images appear to have a greater degree of realness or presence, or `realspace imaging.'' Such topics as high-definition television, 3-D, fisheye lenses, surrogate travel, and `cyberspace'' reflect such interest. These topics are usually piled together and are unparsable, with the implicit assumptions that the more resolution, the more presence, and the more presence, the better. This paper proposes a taxonomy of the elements of real-space imaging. The taxonomy is organized around six sections: (1) monoscopic imaging, (2) stereoscopic imaging, (3) multiscopic imaging, (4) panoramics, (5) surrogate travel, and (6) real-time imaging.

Virtual environments are computer-generated environments with computer-generated objects. These objects will, in general, have interactions. Thus the construction and editing of virtual environments will involve the specification of interactions. This paper presents a way of viewing interactions, the two-point paradigm, which permits the user to view and edit interactions between pairs of objects in real time from within the environment. The two-point paradigm naturally suggests data structures for objects, interaction definition, and the actual interactions in the environment. These data structures are described, and a simple editor based on them is suggested.

A virtual environment system has been developed for viewing and manipulating a model of the human leg. The model can be used to simulate the biomechanical consequences of various reconstructive surgical procedures. Previously, the model was implemented on a standard engineering workstation, and interaction was limited to a mouse and screen cursor. By incorporating the leg model into a virtual environment, the authors were able to assess the value of a head-coupled stereo display and direct 3-D manipulation for a surgery simulation application. This application is an interesting test case for a virtual environment because it requires visualization and manipulation of complex 3-D geometries. Since the model can be used as the basis for a number of biomechanical analyses, the virtual environment provides an opportunity to visualize the resulting datasets in the context of the 3-D model. The components used in assembling the system are described the design and implementation of this system is discussed, and a set of interface techniques that allow direct 3-D interaction with the model is presented.

A high-resolution head-mounted display has been developed from substantially cheaper components than previous systems. Monochrome displays provide 720 by 280 monochrome pixels to each eye in a one-inch-square region positioned approximately one inch from each eye. The display hardware is the Private Eye, manufactured by Reflection Technologies, Inc. The tracking system uses the Polhemus Isotrak, providing (x,y,z, azimuth, elevation and roll) information on the user''s head position and orientation 60 times per second. In combination with a modified Nintendo Power Glove, this system provides a full-functionality virtual reality/simulation system. Using two host 80386 computers, real-time wire frame images can be produced. Other virtual reality systems require roughly $250,000 in hardware, while this one requires only $5,000. Stereo is particularly useful for this system because shading or occlusion cannot be used as depth cues.

This paper addresses the extensions to the image quality metrics and related human factors research that are needed to establish the baseline standards for emerging volume display technologies. The existing and recently developed technologies for multiplanar volume displays are reviewed with an emphasis on basic human visual issues. Human factors image quality metrics and guidelines are needed to firmly establish this technology in the marketplace. The human visual requirements and the display design tradeoffs for these prototype laser-based volume displays are addressed and several critical image quality issues identified for further research. The American National Standard for Human Factors Engineering of Visual Display Terminal Workstations (ANSIHFS-100) and other international standards (ISO, DIN) can serve as a starting point, but this research base must be extended to provide new image quality metrics for this new technology for volume displays.

Previously reported research has illustrated the dependence of stereoscopic utility on the figures of merit selected as well as the display application. This paper reports on a subsequent experiment in which subjects not only judged the relative depth ordering and subjective quality of planar symbols in a 3-D plan view display, but also manipulated a 3-D cursor. The 3-D images were presented on a Tektronix SGS 620 field-sequential stereoscopic CRT (19-inch diagonal, 120-Hz field rate, passive glasses). Three sources of depth information (cue types) were combined factorially to construct exemplary 3-D images: relative size (angular subtense decreased with increasing depth); stereo (binocular disparity varied from crossed to uncrossed with increasing depth); and luminance (luminance decreased with increasing depth). In addition, depth cue salience and display complexity were included in the factorial design. Inclusion of each of the three depth cues produced significantly faster depth judgments, more accurate cursor positioning, and improved image quality ratings. While the use of multiple depth cues had a complementary effect on performance and image quality ratings (i.e., more was better), the effects were clearly interactive rather than strictly additive.

A report on the effects of quantizing stereo pairs computed for stereopsis is presented. Two methods for quantization of color images -- the octree method, which is elegant and fast, and the MaxMin method, which was designed for pseudo-random dithering -- are compared. Their application to stereo pairs, which have been computed using true color (24 bit), can cause anomalies in the resulting stereo image such as loss of depth, contradictory features leading to binocular rivalry, image discontinuities, and loss of definition. Techniques for image sampling to decrease processing time and color lookup table construction to minimize the anomalies are also discussed. A solution for quantizing stereo animations is suggested.

Left to right channel differences of the transmission factors in a 3-D TV system result in asymmetric multiplicative luminance deviations, which can impair picture quality and/or can reduce the visual comfort. Twenty non-expert observers assessed the impairment of overall as well as localized asymmetric deviations (as it may happen, e.g., with lenticular screen displays) in terms of the CCIR impairment scale. The luminance asymmetries were produced by processing the digitized stereo image pair of two natural scenes, according to a reduction of the transfer function of only one channel. Results show that (1) overall and localized luminance asymmetries are perceptible if the transmission factors differ by 3...6 dB, depending on the spatial extension and gradient of the deviation; and (2) if a pattern of a sharply localized luminance deviation is moving (as it may happen, e.g., when an observer moves his head in front of a lenticular screen display), it is perceptible if the transmission factor differs by only 0.2 dB.

With increasing use of three-dimensional stereoscopic display systems, there is a need to define optimal user interface guidelines for these systems. This study examines human performance in two tasks which required participants to view 3-D imagery with or without retinal disparity cues. The imagery consisted of an airspace control zone and it was rendered on the display screen in each of three formats: (1) a plan view, (2) a simple perspective view, and (3) an enhanced perspective view. One task required viewers to judge relative depth positions for objects within the 3-D space, while the other task required extrapolation of object motion headings. Retinal disparity cues reduced both the number and degree of errors, but only for the plan view, course prediction task condition. Not only did retinal disparity cues not provide any performance advantages for perspective displays, but performance levels for these displays were no different than those achievable with a plan view in the absence of retinal disparity cues. Although retinal disparity cues had no effect on search time, the enhanced perspective displays formats effectively increased search times relative to plan view and simple perspective formats. Neither retinal disparity cues nor display format had an effect on subjective ratings of viewer confidence.

Binocular disparity is used on field-sequential stereoscopic displays to enhance monocular depth cues such as perspective, shading, shadows, and interposition. While the predicted apparent depth may be calculated using geometric equations, the actual apparent depth may not follow predictions due to the influence of accommodation and convergence. A study was performed to determine the effect of viewing distance on subjective rating of apparent depth. Viewing distance significantly influenced subjective depth ratings. Displayed objects viewed from greater distances (2678 mm) portrayed greater differences in depth than equivalent displayed scenes viewed from smaller distances (669 and 1339 mm).

The historical development of shutters employed in selection devices used for field-sequential electro-stereoscopic displays is traced. The discussion encompasses mechanical shuttering systems used for motion pictures and vector computer graphics displays, and early electro- optical shuttering systems using PLZT ceramic material. The art of electro-stereoscopy was advanced with the introduction of the surface mode liquid crystal device, which is ten times faster than the prior and more commonly employed twisted nematic device. The types of surface mode devices are described, including those mounted in front of display screens used in conjunction with passive glasses, and the achromatic shutter used in the latest wireless active shuttering eyewear.

An autostereoscopic system is described which permits the observation of a high-resolution image by several persons simultaneously and is suited to mass production. The display uses cylindrical lenses positioned in front of an image output screen. The number of lenses, or the parallax number, determines the number of simultaneous images which can be used to produce a look-around capability. The playback system uses an electro-optical vertical slit which oscillates horizontally within a large horizontal convex cylindrical lens. The resolution of the method is excellent and the parallax number can be varied. Using the transmission band width of HDTV, a five parallax color system with the standard television resolution can be produced.

In early 1990, DTI introduced the first PC-compatible autostereoscopic display product. This LCD based, flat panel, black and white VGA display, called the DTI 100M, was described at the 1990 SPIE conference. During 1990, the company began development of several new capabilities including: (1) a Macintosh-compatible version of its DTI 100M display. (2) a software toolkit for developers that includes a mouse-controlled 3-D cursor and the capability to combine two perspective views generated by many 3-D software packages into a single stereo view. (3) color autostereoscopic displays for its own product line, OEM products, and government contracts. (4) a time-multiplexed autostereoscopic system which allows the observer to see left and right eye images with full-display resolution.

This paper describes the on-going development of a compact zoom lens specifically for stereoscopic television in nuclear environments. Custom-designed optics in radiation-tolerant glass provide a focal length of 12.5 mm to 36 mm with a package length of less than 110 mm. A novel method of encoding the position of the lens elements allows for very compact motorization, and a precision mechanism designed to overcome backlash ensures the stability of picture matching. The position of the lens elements is controlled by a 16-bit microcontroller, and the control strategy allows focus and convergence to be maintained to a high degree of accuracy during zooming.

Many viewing devices have been produced using spinning or oscillating optical elements to artificially enlarge the exit pupils of a stereomicroscope. Further advances have seen the utilization of liquid crystal diffusers so that such devices could operate without moving components. However, the implementations reported thus far have been complex and bulky. The optical system design for a simplified viewing technique is presented in this paper. A standard objective, providing the greater portion of image magnification, is used with an eyepiece which is of a liquid crystal, expanded pupil design. Current limitations in liquid crystal technology prevent eyepiece magnifications greater than 5 X. Therefore, wider fields and higher magnifications are required of the objective lens. Effects of the expansion influence resolution and brightness. Resolution is only minimally reduced as is shown in the experimental results. Brightness reduction can be held to nearly the theoretical limit, but is unavoidable in any system where the exit pupil diameter is increased beyond the eye pupil diameter. As with previous instruments, the advantage of large pupils is the relaxation of eye position constraints. This provides automatic accommodation for interocular variation among users and allows head motion over several centimeters while viewing.

A laparoscope that generates three-dimensional images in real time by the VISIDEPtm technique of alternating frames has been tested. Images from two separate viewpoints are combined through special folded optics and brought out along a single light path where they are viewed with a single eye or with a single video camera. Liquid-crystal shutters are used to alternately switch between the two stereoscopically related views at a rate of 10 Hz in accordance with the VISIDEPtm teachings. The resulting three-dimensional image is autostereoscopic and may be viewed on any standard television monitor. Although the instrument provides for two separate viewpoints, it is built to the same external dimensions as conventional monocular laparoscopes with an outside diameter of 11 mm. This laparoscope can be adapted to field-sequential stereo for presentation of separate images to separate eyes with the aid of electro-optic glasses.

Typical teleoperator display systems to date have relied on standard monoscopic video as the primary feedback link. Research clearly shows that using stereoscopic video (SV) is generally a significant improvement over monoscopic video (MV) for most teleoperation tasks. Abundant as the benefits of SV are, they can be dramatically increased with the superpositioning of stereoscopic graphics (SG) on the SV image. The resulting SV + SG system can greatly enhance the benefits of SV alone in the understanding of a remote world. This combination of media results in an exploration tool uniquely suited for examining different environments, whether remote, microscopic, or artificial. The SV + SG technology can also be used as a command tool that can be used to control manipulators (remote, microscopic, or artificial) in the different environment. A SV + SG system was implemented, and an experiment was performed to determine whether or not SG images were actually perceived as existing at the desired location in the SV view. The experiment compared the performance of a virtual SV + SG Pointer with that of a real-world pointer, and showed that the virtual pointer could be positioned as accurately as the real pointer, with only a slightly higher variance.

The power of today''s supercomputers promises tremendous benefits to users in terms of productivity, creativity, and excitement in computing. A study of a stereoscopic display system for computer workstations was conducted with 20 users and third-party software developers, to determine whether 3-D stereo displays were perceived as better than flat, 2- 1/2D displays. Users perceived more benefits of 3-D stereo in applications such as molecular modeling and cell biology, which involved viewing of complex, abstract, amorphous objects. Users typically mentioned clearer visualization and better understanding of data, easier recognition of form and pattern, and more fun and excitement at work as the chief benefits of stereo displays. Human factors issues affecting the usefulness of stereo included use of 3-D glasses over regular eyeglasses, difficulties in group viewing, lack of portability, and need for better input devices. The future marketability of 3-D stereo displays would be improved by eliminating the need for users to wear equipment, reducing cost, and identifying markets where the abstract display value can be maximized.

A low cost flicker-free field-sequential stereoscopic display has been developed. The system uses commercially available television products developed for the removal of flicker problems associated with the world interlaced television standards. These products reduce overall circuit complexity and implementation costs.

It is the aim of most work with graphics photography and video to create vivid and compelling images. Though telepresence and virtual reality are new terms there exists a vast body of research in stereoscopic vido and other fields with similar objectives. Most of this work has appeared in patent documents or obscure publications and is rarely cited. In order to stimulate research a number of areas of interest are briefly reviewed and accompanied by extensive bibliographies. These include single camera and dual camera stereoscopy cornpatible 3D recording and transmission helmet mounted displays field sequential stereo and head and eyetracking devices.