The difference in accommodation and convergence distance experienced when viewing stereoscopic displays has long been recognized as a source of visual discomfort. It is especially problematic in head mounted virtual reality and enhanced reality displays, where images must often be displayed across a large depth range or superimposed on real objects. DTI has demonstrated a novel method of creating stereoscopic images in which the focus and fixation distances are closely matched for all parts of the scene from close distances to infinity. The method is passive in the sense that it does not rely on eye tracking, moving parts, variable focus optics, vibrating optics, or feedback loops. The method uses a rapidly changing illumination pattern in combination with a high speed microdisplay to create cones of light that converge at different distances to form the voxels of a high resolution space filling image. A bench model display was built and a series of visual tests were performed in order to demonstrate the concept and investigate both its capabilities and limitations. Results proved conclusively that real optical images were being formed and that observers had to change their focus to read text or see objects at different distances
Volumetric displays, in which an image that physically occupies space is built up from many 2D cross sections, has many attractive features including smooth parallax in all directions, coincident focus and fixation points, and wide viewing angles. However, existing volumetric displays require an image forming apparatus that occupies the same volume as the image itself. Large volumetric displays therefore tend to be very expensive and bulky, and may not be practical at all beyond a certain size. DTI has demonstrated optics that can project miniature (about 1 cubic inch) 3D volume filling images into a volume of arbitrary size limited only by the dimensions of a screen-like (i.e. of large area and relatively thin) optical assembly. This greatly reduces the size requirements for the image forming device and its mechanical or optical scanning mechanisms, while producing very large images that can occupy space ranging from the area in front of the display to infinity behind it. The viewing area can be of about the same lateral dimensions as the screen-like assembly, without violating etendue conservation. The optics also simplify the challenges associated with electronic holography, since a very small electronic hologram can be employed as the image source.
DTI has demonstrated a laboratory model of a multiple zone autostereoscopic display with look around capability and a 21' diagonal screen. The display exploits the extremely fast address rates and liquid crystal response speeds associated with ICFLCDs to generate eight to twenty four images during the 1/60th second that a single image is usually displayed. These images consists of the three color components of eight different perspective views of a scene. Optics are used to magnify the images and project them onto a special lens and diffuser screen, which in turn directs light from each image into a different viewing zone in front of the display. Since the perspective views are time multiplexed, each possesses the full resolution of the ICFLCD. An advanced method of generating gray scale using the digital ICFLCD in combination with a time varying light source was also demonstrated. For the most part, off the shelf components were used to construct the key elements of the system including the projection screen and the precision magnifying optics, promising easy commercialization and low production cost. The display is being developed into a prototype, to be followed by production of 1024 X 768 or 1280 X 1024 desktop rear projection display for workstation applications.
At the 1997 conference DTI first reported on a low cost, thin, lightweight backlight for LCDs that generates a special illumination pattern to create autostereoscopic 3D images and can switch to conventional diffuse illumination for 2D images. The backlight is thin and efficient enough for use in portable computer and hand held games, as well as thin desktop displays. The system has been embodied in 5' (13 cm) diagonal backlights for gambling machines, and in the 12.1' (31 cm) diagonal DTI Virtual Window(TM) desktop product. During the past year, DTI has improved the technology considerably, reducing crosstalk, increasing efficiency, improving components for mass production, and developing prototypes that move the 3D viewing zones in response to the observer's head position. The paper will describe the 2D/3D backlights, improvements that have been made to their function, and their embodiments within the latest display products and prototypes.
DTI has demonstrated a backlight for LCDs that creates autostereoscopic 3D with no sacrifice in quality to conventional 2D images. The new backlight is comparable in size and cost to standard 2D backlights and can be manufactured using similar processes. Prototypes have been used in amusement games, LCD desk top monitors, and PC Notebooks. An acrylic light guide accepts light from a miniature fluorescent lamp. Linear structures on one side of the guide reflect light traveling through it toward the LCD. A lenticular lens images the light from the structures into a much larger number of thin light lines within the LCD glass. These lines are spaced in a precise relationship with the pixels of the LCD so that an observer sitting in front of the display sees all the light lines through the odd columns of pixels with the left eye and through the even columns of pixels with the right eye. An electronic shutter is placed between the light guide and the lenticular lens. In the off state the shutter will diffuse the light from the light lines for 2D mode viewing. In the clear state (power on), the light lines are visible for 3D mode viewing.
Experiments indicate that the volume of virtual space within which stereoscopic images can be seen comfortably, without eye discomfort, fusion difficulty, or inaccuracies in perceived depth, is dependent upon the eye to screen distance. This volume is maximized when the screen appears to be at infinity--that is, when it is collimated. With the image collimated, objects located within a virtual space extending from a few feet in front of the observer to infinity can be viewed comfortably. Collimation also reduces the distortion seen in stereoscopic images when viewing them from off axis locations. DTI is developing two magnified and collimated autostereoscopic displays. One uses a collimation module designed for out the window simulators to provide a very wide angle, immersive image that is potentially well suited to flight simulators and video games. Another, more compact version uses Fresnel lenses to magnify the images of a high resolution 13.8" diagonal LCD to the same angular size as a 21" display seen at 30". This variation may be more suited to desktop displays. It provides resolution, color palette, and apparent screen size equivalent to a high end CRT.
Autostereoscopy is finding acceptance in applications where stereoscopic imaging is critical and where the use of stereo glasses and virtual reality head mounted displays is unacceptable. A wide variety of telerobotic activities are beginning to rely on autostereoscopic displays for visual input. Experimental applications have been found in industrial inspection and sign language learning/communication.
The use of an autostereoscopic display (a display that produces stereoscopic images that the user can see without wearing special glasses) for cockpit applications is now under investigation at Wright Patterson Air Force Base. DTI reported on this display, built for testing in a simulator, at last year's conference. It is believed, based on testing performed at NASA's Langley Research Center, that collimating this type of display will accrue benefits to the user including a grater useful imaging volume and more accurate stereo perception. DTI has therefore investigated the feasibility of collimating an autostereoscopic display, and has experimentally demonstrated a proof of concept model of such a display. As in the case of conventional displays, a collimated autostereoscopic display utilizes an optical element located one focal length from the surface of the image forming device. The presence of this element must be taken into account when designing the optics used to create the autostereoscopic images. The major design issues associated with collimated 2D displays are also associated with collimated autostereoscopic displays.
Over the past two years, DTI has developed technology under an SBIR program designed to create advanced autostereoscopic hologram-like displays yielding multiple full resolution perspective images that can be viewed passively by multiple observers across a wide area. The first prototype display of this type was completed in 1994. It demonstrated three key technologies necessary for the practical embodiment of an advanced commercial flat panel autostereoscopic display. (1) A fast surface mode LCD capable of displaying 180 images per second with many gray levels. (2) An interlaced light line illumination system that is responsible for making different images visible from different regions of space in front of the display, and allows flicker free imaging at near 30 fps. (3) A controller designed to accept perspective images in standard formats, interlace them, and display them on the LCD. These technologies are demonstrated on an 800 X 400 LCD with 32 true gray shades, yielding up to six perspective views every 33 ms. At half resolution it would be possible to generate twelve views. The system is driven by an entry level workstation and could also accept input from multiple cameras, given the right interface. Results of the project and plans for the future will be discussed.
DTI has demonstrated new optical configurations designed to project autostereoscopic images to very large sizes using only one display and projector. They will allow the creation of large (50 cm and greater) immersive high resolution autostereoscopic displays with advanced features like head tracking and/or look around imaging. Previous autostereoscopic projection devices have used multiple displays in combination with multiple projectors, with attendant complexity and expense. The basic technique uses a small LCD to create viewing zones within a single large projection lens, of the type normally used for projection television applications. The lens images the LCD onto a large Fresnel lens. The Fresnel lens in turn re-images the viewing zones into the space in front of it. In this arrangement, the viewing area is limited to roughly twice the size of the lens that is used for projection. Methods used to expand the viewing area will be described.
Mounting a lenticular lens in front of a flat panel display is a well known, inexpensive, and easy way to create an autostereoscopic system. Such a lens produces half resolution 3D images because half the pixels on the LCD are seen by the left eye and half by the right eye. This may be acceptable for graphics, but it makes full resolution text, as displayed by common software, nearly unreadable. Very fine alignment tolerances normally preclude the possibility of removing and replacing the lens in order to switch between 2D and 3D applications. Lenticular lens based displays are therefore limited to use as dedicated 3D devices. DTI has devised a technique which removes this limitation, allowing switching between full resolution 2D and half resolution 3D imaging modes. A second element, in the form of a concave lenticular lens array whose shape is exactly the negative of the first lens, is mounted on a hinge so that it can be swung down over the first lens array. When so positioned the two lenses cancel optically, allowing the user to see full resolution 2D for text or numerical applications. The two lenses, having complementary shapes, naturally tend to nestle together and snap into perfect alignment when pressed together--thus obviating any need for user operated alignment mechanisms. This system represents an ideal solution for laptop and notebook computer applications. It was devised to meet the stringent requirements of a laptop computer manufacturer including very compact size, very low cost, little impact on existing manufacturing or assembly procedures, and compatibility with existing full resolution 2D text- oriented software as well as 3D graphics. Similar requirements apply to high and electronic calculators, several models of which now use LCDs for the display of graphics.
This paper describes the cockpit display, its properties and capabilities, and how the technology proven on this display is being incorporated into commercial autostereoscopic devices.
Dimension Technologies Inc. has experimentally demonstrated an optical system that produces autostereoscopic images and also allows very high brightness and power efficiency to be achieved using off the shelf color LCDs. This capability is important in applications such as cockpit displays or mobile, portable, or laptop systems where brightness must be maximized but power conserved as much as possible. The effects are achieved through the creation of light line illumination, by means of which autostereoscopic images are produced, and by simultaneously concentrating the light emitted by the display toward the area the viewer's head is. By turning different illumination sources on and off, it is possible to aim both the concentration area and the 3D viewing area at the observer's head as the observer moves. A variation on the system allows two or more persons to be tracked independently. Cross talk (ghosting) can be reduced to the point that imperceptibility can be achieved.
Dimension Technologies Inc. has devised and experimentally validated a technique for producing field-sequential-color illumination for liquid crystal displays (LCDs) that does not exhibit image breakup and can provide flicker free images at slower refresh speeds than other field-sequential-color techniques. The technique involves a combination of colored illumination patterns that are sequentially imaged within the pixels of an LCD. An optical bench version of this type of illumination system was used to evaluate the ability to produce white light, evaluate flicker performance, evaluate image breakup visibility, and perform reading tests. This work can lead to a superior means of producing color displays using monochrome LCDs. Application of the research by LCD manufacturers may allow that industry to produce simplified, less costly LCDs for color displays.
Matrix addressed liquid crystal (LC) light valves are exerting an ever increasing presence in both direct-view and projection mode display sectors. In transmissive mode the periodic structure of the matrix, when used in conjunction with a backlighting source capable of temporal and spatial modulation, offers the capability to obtain autostereopsis in a useful and economic fashion. This novel combination of complex and proprietary illumination mechanisms with matrix addressed LC valves has been researched and practically validated by the author and various useful configurations defined. From this it has been established that stereoscopic displays can be obtained without either compromise to display surface resolution or requiring the viewer to employ complementary optical devices. The work performed to date has further confirmed that such display constructs may be usefully applied to direct view, projection mode, and helmet mounted systems to the net benefit of operator performance.
During 1992, Dimension Technologies Inc. (DTI) completed several development projects designed to enhance and improve its autostereoscopic display technologies. These include: The introduction and upgrading of a very bright 640 X 480 full color autostereoscopic display with user controlled selection of 3D or 2D viewing modes. Development of an electronic head tracking system that allows a user to observe stereo from across a wide area without head position restrictions. Development of a 640 X 480 autostereoscopic color display that allows each of the observers eyes to sell all the pixels on the LCD. Initial development work on a compact display designed to provide look around on high resolution images using multiple perspective views.
Dimension Technologies Inc. (DTI) has devised and experimentally tested a new photonics system which will allow the display of images on LCDs with resolutions greatly exceeding the pixel resolution of the LCD. The technique involves use of special lenses to successively image light from an array of sources into different subregions of pixels on a fast operating LCD, creating a high resolution image made up of the light points. The technique was successfully used to create 308 dpi images on an experimental 154 dpi ferroelectric LCD. Field sequential color illumination can be combined with this technique to create high resolution color images. Using this technique, it is possible to create very high resolution images without using a correspondingly large number of pixels on an LCD, thus avoiding manufacturing and yield problems associated with high resolution LCDs.
Rapid development in imaging technology has made useful and affordable solutions possible for applications requiring operation and analysis of remote and virtual environments. Research in human and machine vision has shown the importance of stereopsis (depth perception) in the vision process. Empirical research also has shown the benefits of stereopsis in teleoperation tasks through the use of stereoscopic display technology. The practical value of this technology for real-world applications can be greatly improved through the use of unobtrusive autostereoscopic displays. This applied research explores the various applications of teleoperation, specifically those in which stereo vision is of critical importance. Investigation of stereoscopic imaging system requirements and properties helped identify areas which could potentially benefit from such a system. A testing site using a remotely operated underwater vehicle was used to perform empirical experiments to evaluate the performance benefits derived from the use of the autostereoscopic display. These results were used to define more formal experiments which were conducted. Ergonomic issues associated with the display were also explored through a subjective user survey.
Dimension Technologies is currently one of three companies offering autostereoscopic displays for sale and one of several which are actively pursuing advances to the technology. We have devised a new autostereoscopic imaging technique which possesses several advantages over previously explored methods. We are currently manufacturing autostereoscopic displays based on this technology, as well as vigorously pursuing research and development toward more advanced displays. During the past year, DTI has made major strides in advancing its LCD based autostereoscopic display technology. DTI has developed a color product -- a stand alone 640 X 480 flat panel LCD based 3-D display capable of accepting input from IBM PC and Apple MAC computers or TV cameras, and capable of changing from 3-D mode to 2-D mode with the flip of a switch. DTI is working on development of a prototype second generation color product that will provide autostereoscopic 3-D while allowing each eye to see the full resolution of the liquid crystal display. And development is also underway on a proof-of-concept display which produces hologram-like look-around images visible from a wide viewing angle, again while allowing the observer to see the full resolution of the display from all locations. Development of a high resolution prototype display of this type has begun.
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.
. Dimension Technologies has developed a black and white 640 X 480 pixel flat panel autostereoscopic computer monitor that interfaces with the IBM PC family of comouters and most comoatibles. A Mac version is under develooment. The monitor emDloys a iiauid crystal dlsDlay as the ''mage generatng element. The LCD s used in combination with a patented illumination system to or-oduce vivid stereoscooic images that can be seen by several observers from several locations in front of the screen. This oaoer describes the monitor and how it works. the advantages of DT s autostereoscoic technology. and the results achieved wth the monitor as a disoiav for comDuter-qenerated maqe and still television images at DT and at customer stes. Aications for stereo dislavs are reviewed. New develoornents are also described. 1.
Dimension Technologies has developed a black and white 640 X 480 pixel flat
panel autostereoscopic computer monitor that is compatible with the IBM PC family of
computers and most compatibles. The monitor employs a liquid crystal display as the
image generating element. The LCD is used in combination with a patented
illumination system to produce vivid stereoscopic Images that can be seen by several
observers from several locations in front of the screen.
This paper describes the monitor and how It works, the advantages of DTI's
autostereoscopic technology, and the results achieved with the monitor as a display
device for computer generated images and still television images.
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