AUTOSTEREOSCOPIC DISPLAYS USING LENTICULAR SCREENS
Autostereoscopic displays are those which do not require the user to wear viewing aids. Displays using lenticular screens have been the subject of intensive research for nearly 80 years. The two Ives laid the foundations (US 666424, 725567, 771824, 1262954, 1814701, 1882424, 1883290, 1883291, 1905469, 1905716, 1916320, 1918705, 1937118, 1960011, 1970311, 1987443, 2002090, 2011932, 2012995, 2039648). Hundreds of researchers followed and there are perhaps 2000 patents and several hundred technical papers on the use of lenticular screens and related means for photography, motion pictures and television. It is impossible to cover more than a few of the more prominent or recent which relate most directly to video. Photographic systems have become common with both professional and consumer lenticular cameras. Motion picture applications have been rare with only the Russian lenticular glass screen being publicly shown in the USSR and at the Osaka Expo in 1970. Eight years before his invention of Holography in 1948, Gabor filed three patents on lenticular methods for movie projection(US 2351032,2351033,2351034) and in 1953 he filed what is probably the longest and most detailed patent ever granted on autostereo projection(GB 750911). Remarkably, later researchers seem to have almost completely ignored this work and even Gabor in his 1969 patent on holographic movie projection(US 3479111) fails to reference his last and most complete patent on this topic.
. Lenticular television devices have been prototyped many times but whether the screens were inside the CRT( Wallman, JAP 58-38093) or on the front of the faceplate or projection screen(e.g., Yanagisawa), alignment of pixels with lenslets was a major problem. Makoto Kikuchi of Sony pursued this approach vigorously during the 80’s(JAP 53-20347, 56-126235, 56-126236, 56-128085, 56-128086, 56-132752, 56-134895, 56-168326, 57-3487, 57-11592, 57-13886, 57-14270, 57-17546, 57-18189, 57-26983, 57-27544, 57-27545, 57-27546, 57-67393, 57-72250, 57-75090, 57-83990, 57-83991, 57-87291, 57-106291, 57-123787, 58-29283, 58-31692, 58-103285, 58-115737). Tripp(US 3932699) was probably the first to build an adequate system, solving the alignment problem with a 13 inch diagonal fiber optic faceplate with a vertical lenticular screen. The input was a one inch camera tube covered with a specially made lenticular screen having 525 lenticulations per inch. This was made from a metal master hand engraved with the aid of a microscope(the same technique used to engrave dollar bills). This was perhaps the best autostereo CRT based system to date, but it was never duplicated and was soon cannibalized for the expensive fiber optics. Tripp however is a very flexible and ingenious man(one of his early inventions was the escalator) and he claims to have recently invented an extremely high resolution(2000 line pairs/mm) “spatial hologram without lasers” intended for use with his high resolution low dose x-ray system.
The advent of flat panel displays, which do not have the problem of aligning pixels and lenticules through an intervening layer of glass is resulting in renewed interest in this approach(Ichinose). Work is ongoing in France(US4584604), England(Sheat) and Japan(Tetsutani et al.) on a system for a 3D picturephone.
Another problem is that it is desirable to have a large number of these laterally multiplexed stereo pairs to minimize image “flipping” and give a “look around” capability(Schwartz). However, with most of these autostereo techniques, resolution and number of views are inversely related. With a 0.5mm lens size and 50 views, one needs a resolution of 10 microns, near that used for holographic plates and certainly beyond that of any available video display(with the possible exception of some of Tripp’s prototypes). When it becomes possible to interpolate many views from a stereo pair, it will stimulate the whole field of autostereoscopy. Scene interpolation has been the subject of much research for robotics and pattern recognition but only a few workers have attempted to apply this directly to autostereoscopic display(Oshima and Okoshi).
Front or rear projection of stereo with lenticular screens has been investigated by many but has rarely resulted in commercial product. Sanyo Corp. has shown large rear projection lenticular systems in 1994 and offered a 50 inch diagonal model for $50,000. Image quality was modest and restriction on head position severe. Joji Hamasaki in Tokyo has been one of the most persistent and successful in this work with multiple video projection and large diameter screens as well as with the Sony beam index CRT(JAP 61-77839, Hamasaki). NHK and other has an active program with multiple LCD rear projection on a Toppan Corp. plastic lenticular screen(Isono). Viewing distance is limited to about 3 meters plus or minus 10cm and careful head positioning is necessary to avoid pseudoscopic zones(problems for all lenticular systems). Hamasaki’s efforts and those of NHK are shown on the 3D videotapes “3D TV Technology Vols 1 and 2” marketed by 3D TV Corp. A vigorous program was conducted at the Heinrich Herz Institute in Berlin with front and rear projection on lenticular screens custom made by Philips in Eindhoven(Borner). Philips has extremely high precision computer controlled diamond milling equipment for making lenticular screens for their videoprojectors. A 1500 line screen can be milled in a plastic master in about 2 hours and the poured acrylic screen rapidly cured with uv . Minute corrections in the screen can be reliably programmed, engraved, cured and ready to test in one day for a one time set up fee of about $25,000 and a cost of about $20,000 for a 1M by 1M pair of screens in prototype quantities. This process used to take months and was not very accurate. The final screen is accurate and repeatable to one micron. Dr. Schmitz demonstrated this by making a screen which copied the eye of a bee and proved its extreme accuracy with electron microscope photos. This may result in commercial lenticular systems in the next few years.