TECHNICAL PAPER The Stereoscopic Cinema: From Film to Digital Projection By Lenny Lipton Lenny Lipton A noteworthy improvement in the projection of stereoscopic moving awaited the invention of commercial- images is taking place; the image is clear and easy to view. Moreover, the quality sheet polarizers by Edwin setup of projection is simplified, and requires no tweaking for continued Land, who applied the material to 3 performance at a high-quality level. The new system of projection relies stereoscopic eyewear. on the Texas Instruments Digital Micromirror Device (DMD), and the The Norling approach became the model for the theatrical motion pic- basis for this paper is the Christie Digital Mirage 5000 projector and ture stereoscopic boom of the early StereoGraphics selection devices, CrystalEyes and the ZScreen. 1950s. In those days theaters had two projectors in the booth for changeover from reel to reel, provid- tereoscopic cinema has not problems of the past to better appreci- ing an opportunity to modify the Sbecome an accepted part of the ate the virtues of the improvement setup to run interlocked left and right neighborhood theatrical experience described. projectors (Fig. 1). because the technology hasn’t been Polarization Efforts It may well be that problems in the perfected to the point where it is satis- projection booth bear the major share fying for either the exhibitor or the The first successful (and influential) of responsibility for this short-lived viewer. However, the medium has commercial use of full-color stereo- effort. Polaroid researchers Jones and become widely accepted in theme scopic movie projection in the U.S. Shurcliff4described the artifacts relat- parks and location-based entertain- was in 1940 (a similar film was pro- ed to projector synchronization and ment where some of the problems jected in monochrome in 1939) at the shutter phase. The same kind of dual- have been overcome. For the most World’s Fair in New York. John A. projector scheme is used in today’s part, the projection technology used in Norling produced and photographed a theme parks. The theme park theater theme park theaters is identical to that film showing the assembly of a is more manageable than a neighbor- first employed commercially in 1939: Chrysler automobile. The film was hood theater, since more diligence can two projectors run in interlock with shot with a 35mm camera rig and pro- be devoted to making a touchy system lenses projecting through sheet polar- jected with a pair of projectors in work. izer filters. Audience members wore interlock. As mentioned, polarization polarizer analyzer eyewear for image was used for image selection.1 Single Projector Methods selection (the means for getting the The film debuted some four The history of the cinema teaches left eye image to be seen only by the decades after the suggestion was first that systems requiring multiple left eye and vice versa). made for using polarization as a machines, for color, sound, or wide- It is expected that digital projec- method of image selection. This delay screen, will be displaced by single tion, which produces a clean ghost- from idea to successful implementa- projector solutions. The same factors free image and requires the use of tion is typical of technology in gener- apply to the stereo-cinema. For exam- only one projector, will undoubtedly al, and the stereoscopic medium in ple, in the early 1980s, attempts were usher in a new and superior version of particular, in which innovation has made to commercialize single projec- the medium. First, let us take a histor- sometimes depended upon the arrival tor methods that placed left and right ical detour in order to understand the of new enabling technologies. In this images above and below each other case John Anderton2first suggested with Techniscope-style (two perf polarization for selection using the high) subframes.5Special dual optics A contribution received on April 26, 2001. Lenny Lipton is with StereoGraphics Corp., San Rafael, CA cumbersome piles-of-plates tech- that incorporated polarizing filters 94901. Copyright © 2001 by SMPTE. nique, but a viable implementation were required for projection.6 586 SMPTE Journal, September 2001 • www.smpte.org THE STEREOSCOPIC CINEMA: FROM FILM TO DIGITAL PROJECTION In the early 1980s a few films were shot and released using this approach. Unfortunately, one set of difficulties Screen had been replaced with another: this subframe method is considerably less bright than the dual-projector method. Polarizing It was introduced at a time when Filter screen sizes were larger than ever and more brightness was needed. In addi- tion, while synchronization of two projectors was not an issue, it was too Left easy for the projectionist to splice reels together at the subframe line rather than at the frame line. The Right result is the projection of a pseudo- stereoscopic image. The viewing of a left perspective Polarizing view with the right eye and vice versa Glasses does not happen in the visual world; people have a hard time articulating the nature of the problem. The result Figure 1. Polarization image selection. Sheet polarizers are used over the projection lenses of this mistake is the destruction of and as analyzers in eyewear. Projection screen must conserve polarization. the raison d'être of the medium caus- ing audience discomfort. This sub- frame technique has more or less fall- en by the wayside, not having been able to live up to its promise. Anaglyph and Vectograph In addition to the polarization method, two other technologies have been considered for theatrical stereo- scopic projection, both of which offer a single projector solution. One, the anaglyph, employing complementary colored images, with selection eye- wear using similar complementary colored filters, has a long history of on-again/off-again use since the early days of the motion picture industry. Although it requires only one projec- tor, a monochrome image and eye fatigue have precluded its acceptance. The Vectograph, a trade name of the Polaroid Corp., was another con- tender, and it has interesting similari- ties to the anaglyph, except that it allows for full color (Fig. 2). At a spe- cial session of Siggraph about a decade ago, a test reel produced by Polaroid in conjunction with Technicolor was shown in a Manhattan screening room. The Figure 2. Vectograph projection. A single film contains both left and right images with each image was extremely bright and sharp having the ability to polarize light. This drawing is from a 1942 patent by Land. with excellent stereoscopic effects. SMPTE Journal, September 2001 • www.smpte.org 587 THE STEREOSCOPIC CINEMA: FROM FILM TO DIGITAL PROJECTION The Vectograph process imbibes open and close in synchrony with the result is a flicker-free stereoscopic polarizing dyes onto two reels of spe- projector shutters. moving image (Fig. 3). cially prepared film that are then Laurens Hammond9invented the It’s not surprising that this method cemented together.7This duplitized first commercial motion picture works, because it is an extension of process was never used commercially eclipse system, Teleview, used in the basic motion picture technology. The for motion picture projection. screening of the movie MARS,at the interrupting projector shutter occludes Selwyn Theater on Broadway in New the film as it is transported, to prevent Eclipse Technique York City in 1923. Mounted on the travel ghost, and also interrupts the Another approach worthy of atten- back of every seat in the theater was projected frame when it is at rest, to tion, because it is the basis for the an adjustable gooseneck, and mounted increase the repetition rate of the pro- improvement in technology described on the gooseneck was a spinning jected fame in order to satisfy the crit- here, is the eclipse or occlusion mechanical shutter in electrical syn- ical flicker frequency condition. The method. It has a great deal in common chronization with the projector’s shut- result is that half the time the viewer with the polarization projection tech- ters. When the pie-shaped shutter’s is observing “nothing” on the screen, nique since both use dual interlocked movement uncovered the right eye, since the image is blocked. The projectors. It was first proposed in the right projector shutter was also stereoscopic occlusion technique fills 1855 for the projection of slides,8 open. At that moment the viewer’s in the periods of nothing with image. requiring the images for the left and left eye was blocked, so was the left Until IMAX’s revival of the right eyes to be alternately blocked projector lens. As the viewer shutters process for dome projection, Teleview and passed. The projector shutters are continued to rotate, the left view was was the only commercial use of this out of phase with each other, and the unblocked and so on and so forth. If motion picture process for over 60 shutters used in the selection devices the repetition rate is high enough the years. IMAX’s addition was the use Figure 3. Teleview theater setup. Spinning shutters cover projector lenses and the viewers’ eyes. The drawing is from the 1924 patent by Hammond. 588 SMPTE Journal, September 2001 • www.smpte.org THE STEREOSCOPIC CINEMA: FROM FILM TO DIGITAL PROJECTION of liquid crystal shutters for the selec- Binocular Symmetries Accommodation and tion eyewear, an approach that had In addition to the ghosting issue, Convergence (A/C) been used for some years for stereo- there are other factors that determine There is another phenomenon pecu- scopic computer graphics. the visual experience one will have at liar to the display of plano-stereoscop- Ghosting a stereoscopic movie. These factors ic images (a stereo image made up of need to be understood to grasp the planar left and right perspective The cross-talk artifact of polariza- extent of the improvement resulting views) that may detract from the tion image selection is one of the art’s from the digital projection technique enjoyment of the image.