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[Kahaner] 3D displays, Sanyo
From: David Farber <farber () central cis upenn edu>
Date: Mon, 26 Dec 1994 08:45:26 -0500
From: Dr. David K. Kahaner US Office of Naval Research Asia (From outside US): 23-17, 7-chome, Roppongi, Minato-ku, Tokyo 106 Japan (From within US): Unit 45002, APO AP 96337-0007 Tel: +81 3 3401-8924, Fax: +81 3 3403-9670 Email: kahaner () cs titech ac jp Re: 3D Displays 12/26/94 (MM/DD/YY) This file is named "3d-displ.94" ABSTRACT. Several examples of 3D display technology in Japan from Sanyo, Matsushita, and Terumo. I have been interested in three dimensional display technology for several years, see for example "fujitsu.3d" 25 April 1990, "3d-2-92.1" and "3d-2-92.2", 19 Feb 1992, and especially the second report for background. Portions of that are reproduced below for completeness. It is useful to make the distinction between 3D, biplano-stereoscopic, and multiplano-stereoscopic images (the latter two are commonly called "stereo"). True 3D images not only give the sensation of depth, but allow observers to "look around" to their sides and perhaps even their back. Biplano-stereo images are produced from (only) two original images. They also can give a very realistic sensation of depth, but have no "look around" capability. An observer moving his/her head while viewing a stereo image causes the image to shift slightly, but no occluded visual information comes into view and the perspective remains the same. Multiplano images are composed of more than two original images and do have some look around capability. Often, the distinction between 3D and stereo images is ignored. Indeed, there are "3D" and even "4D" workstations on sale but this almost always means three dimensional images projected onto a two dimensional display device such as a CRT. Most stereo systems use a stereogram, left and right image pairs, to recreate the depth sensation of binocular vision (stereopsis). The majority of these systems require a device to be worn by the observer to select the image to be viewed by each individual eye. Systems without such an observer-worn selection device are called autostereoscopic, or "glassless". In viewing the real world it is known that the sense of depth is the result of a ten or more different factors. For example, overlapping or occlusion, where one object obscures part of another, is a depth clue that does not depend on having two eyes. Another monocular clue is the image of road edges that we expect to be parallel. Similar monocular clues are related to retinal image size, areal perspective, shading, shadows, texture, etc. An important binocular clue to distance from the observer is the difference in angle between the viewing axes of left and right eyes when both are focusing on a point (convergence). Adjustment of the focal length of the crystalline lens (accommodation) is another clue, although this is mostly monocular. Binocular parallax is the most important binocular clue, relating to the fact that each eye sees a slightly shifted view of the image. Individuals differ greatly in their ability to use these clues either because of physical impairments, training, or some processing difficulties. This is much like color vision; people who lack it entirely discover so at an early age, others whose abilities are below average may go through their entire lives accommodating in other ways. Images can be viewed on electronic displays such as TVs, CRTs, flat panels, etc., or in hard copy form such as a photograph, plot image, and so forth. Viewing images may or may not require the use of special glasses. Anaglyph images require red/green glasses as selection devices, and most people are familiar with these from the large number of commercial motion pictures (in the 1950s and 60s) which required them, but their use can be traced back to as early as 1858. Anaglyph techniques can be used for viewing either still images on paper or dynamic images such as films. However, the current trend for films, video tape or computer screen images has been toward polarized glasses as selectors, or systems without glasses. Current work seems to be primarily directed toward stereo vision, although the main technique for full 3D imaging is holography, i.e. the reconstruction of the object wavefront. The original principle involves illuminating the object with a laser and simultaneously recording the reflected (or diffused) light from the object and a reference beam from the laser, creating an interference fringe pattern. The recorded pattern can later be illuminated with the same laser to reproduce the image. Work in holographic techniques has recently focused on using conventional light rather than a laser, and the creation of holographic stereograms, in which multiple images of an object are recorded by ordinary cameras at different positions and a hologram of each image is recorded sequentially. Holograms can provide a very high resolution and geometrically accurate image which can be viewed without glasses and in principle are indistinguishable from the original object. But initial enthusiasm for holography notwithstanding, practical problems such as reproducing color and providing dynamic displays have not yet been effectively solved. Also, many techniques for holographic imaging produce images smaller than observers would like to see. As one researcher commented, holograms provide too much information, i.e., it isn't really necessary to completely reconstruct the wavefront to have an effective image. However, some of the most exciting developments in this area are being carried out at MIT's media lab under the direction of Prof Stephen Benton. Benton's early claim to fame was the invention of the white light transmission (dubbed rainbow) hologram, and more recently, the practical demonstration of holographic video. The lab is also working on holograms that are in full color, large size, animated, and can be totally synthesized by computer. Perhaps most importantly, this work has re-energized the field and forced researchers to take a more serious look at ongoing related work. In my 1992 report I stated that "we are still years away from practical holography in our homes such as holographic TV. For example, any practical holographic display device relying on Benton's approach will require time-bandwidth product far exceeding those available with single channel acousto-optic modulators, and require other techniques such as multichannel modulators, parallelism, etc." However, NTT has recently announced the development of a prototype holographic movie system. Quoting from the NTT Review, Vol 6 No. 6, Nov 1994, "NTT has realized a system that utilizes 35mm holographic film already on the market to continuously photograph 3D video pictures. The usual 3D movie has a fixed viewing direction and is stereoscopic only on one side, which is not realistic in the real world. However, holography makes it possible to observe from any direction, and to photograph or reproduce a subject in all directions. In also allows the eye to focus on any portion of the image, which provides for a more natural three dimensional picture. However, electronic display devices for holography have not yet reached the level of practical use, so a practical electronic animated holographic picture system has yet to be developed. "To collect the various basic data required prior to practical use of an animated holographic picture system, NTT has developed equipment capable of holographic photography/reproduction in real time as experimental equipment for simulation. "The system developed at this time consists of a photographing mechanism plus a laser light source. For holograms that record more than 1,000 interference fringes per 1mm interval, it [normally] takes a few minutes to photograph each frame using a normal light source because the photographic sensitivity is very low. This [new] equipment, however, uses a strong light source to enable continuous photographing of 3D video pictures on film in real time. "This experiment confirms that the natural movement of difficult substances, such as flowing liquid or trailing smoke, can be faithfully photographed and reproduced. The new system enables existing movie equipment to be used to holographically photograph and reproduce 3D movies of long duration. It is expected to find a wide range of applications in entertainment, medical use, etc., in the future." [end of NTT remarks] If right then left eye images are displayed sequentially from a source, and a synchronized shutter system in front of the eyes allows the right eye image to only enter the right eye, etc., then stereo vision can be observed. The shutter can be mounted in glasses which are matched with a display in which two constituent pictures are presented in alternation instead of simultaneously. The glasses occlude one eye and then the other in synchronism with the image presentation. This is often called "field sequential". This method avoids the retinal rivalry caused by anaglyph viewing but can introduce other discomfort such as the increase of flicker (on 60 Hz displays), the introduction of time parallax between the two images, or the possibility of "ghosting" between the images due to phosphor persistence. On computer displays flicker can be solved by increasing from 60 to 120 frame refreshes per second, although this is accomplished by halving the number of pixels that are painted per frame, perhaps leading to lower resolution. Most glasses-based shutter systems use LCDs which work with polarized light. Currently, glasses using LCDs can provide good switching speed and reasonable extinction of the alternating lenses. The electro-optical polarizing shutters now in use transmit about 30% of the unpolarized input light (rather than 50% for perfect polarizers) and this reduces the image brightness a little, but in practice this does not appear to be a major problem. Some eye-glass shutters are connected by wires to the monitor (tethered), others are controlled by infrared and are wireless. Another system uses a polarizing shutter mounted on the display device and eye-glasses with fixed (circularly) polarized lenses. While this reduces the complexity of the eye-glass system, the large screen-covering shutter is expensive to produce and is fragile. In 1982, C.Smith wrote that "future generations will be astonished that for a few decades in the 20th century we were happy to accept these small flat images as a representation of the real three-dimensional world." It seems obvious that in robotics, photogrammetry, pattern recognition, etc., three dimensional imaging would be a great help. In Japan, work in stereo and 3D imaging spans the same broad subfields as in the West except that there is a decided difference in emphasis. The Japanese have been much more active in research concerning autostereoscopic imaging. Early research work was mostly connected with lenticular sheets and that continues, but today there is also a growing Japanese interest in holography inspired by the impressive work at MIT. The basic idea in this approach (lenticular sheets) is also not new. An object is photographed with two cameras corresponding to left and right eye. Then images are displayed on a sequence of narrow vertical stripes, left eye image, right eye image, left, right, etc., a corduroy or interdigitated display. These days flat panel display devices are often used for the displays. Immediately in front is an array of half cylindrical lenses roughly matching the pitch of the display with axis of revolution from top to bottom of the screen. Out in front of all this sits the observer, who can have an authentic stereo image if he/she is positioned in exactly the right place. Little head movement is allowed and the observer must be seated at exactly the right position. Multiple observers can view this kind of display at the same time although each observer must be correctly positioned. Also it is possible for observers to get a pseudostereoscopic image (right image to left eye, and left to right). All researchers would like to dispense with glasses, but most (Westerners I spoke to) believe that practical systems will require them for the remainder of this decade. At the moment, the main problem with practical autostereoscopic systems (nonholographic) is that the viewing position can be critical. In 1992, one American remarked to me that he didn't understand why there was so much Japanese interest as there seemed to be major technical problems, and there might even be a wall that could not be breached. Another commented that he found that the difficulties encountered when moving from viewing lobe to viewing lobe (i.e., head movement) in glassless lenticular systems to be far more problematic than properly presented glasses approaches. A third said that he saw no Japanese systems that were anywhere near being productizable, and some that were much more than a decade away. In 1992 I stated that "my own view is somewhat different. The problem of stereo or 3D imaging is old enough that many fundamental ideas have already been proposed. Some of these may have failed in the past because the implementation technology was not up to the demands placed upon it. But it may be appropriate to look more carefully again. Even in the case of restricted viewer position, there are obvious applications, such as sitting in front of a computer monitor looking at the image of a molecule." Sanyo has now (1994) released several 3D autostereoscopic systems as products including two large screen models (40 inch and 70 inch, selling for US$100K and US$50K) using a pair of LCD rear mounted projectors and lenticular screens, and three small models using self contained LCD displays (10, 6, and 4 inches, no selling price announced) using an image splitter (parallax-barrier) technique. Some of this technology was developed jointly with NHK (see my report mentioned above for further discussions of NHK's research). I viewed all the systems and found them to be as bright and clear as more traditional displays. Viewing position is important, as expected. Sanyo feels that there are very natural applications in game/entertainment/simulation/museum situations, as well as in selected commercial demonstration fields. Sanyo also believes the smaller systems can be installed in both car and aircraft where head movement is constrained. One specific application mentioned was to add 3D to the growing number of navigational map displays (in autos). In addition to the displays, Sanyo has also developed and is marketing an add-on board that converts ordinary 2D video images to pseudo-stereo 3D by use of a modified time difference algorithm. The board digitizes a linear sequence of image signals from conventional video software for division into two image signals (L and R). The R signal is stored briefly in a video memory and then reproduced on the display a short time after L is displayed. The time lag yields parallax or position shift in the image displayed to the left and right eyes, and gives the appearance of stereo. Since this hardware (board plus 3D LCD display) can be used with any video signal, Sanyo envisions customers viewing their favorite TV shows, but now in "3D". My hosts for the visit to Sanyo were Mr Kenji Oyamada Manager, Hypermedia Research Center Multimedia Systems Department Sanyo Electric Co., Ltd 1-1 Dainichi Higashimachi Moriguchi City, Osaka 570 Japan Tel: +81 6 900-3519; Fax: +81 6 901-6844 and Mr Kenji Taima Sanyo Electric Co., Ltd 3D Project 1-1 Dainichi Higashimachi Moriguchi City, Osaka 570 Japan Tel: +81 6 900-3511; Fax: +81 6 900-3536 Email: KENJI () IMAGE-LAB OR JP or KENJI () YDI-01 YD HM RD SANYO CO JP Another autostereoscopic display device was shown by the Terumo Corp, a medical instrument maker. The company has been working in this field for several years, using time interlacing, a large format convex lens in front of the display and infrared lighting, combined for the stereo effect, in collaboration with Nagoya University College of Medicine. Stated commercial applications include a two camera laparoscope and endoscope. For information about Terumo, contact the following. Mr Tomohiko Hattori at Medical Device Department II Terumo R&D Center Terumo Corp 1500 Inokuchi, Nakai-machi Ashigarakami-gun, Kanagawa-ken 259-01 Japan Tel: +81 465 81 4155; Fax: +81 465 81 4158
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