Since the early days of cinema, engineers and scientists have tried to create a way to add the illusion of depth to projected images. Even with the latest technology, cumbersome 3-D glasses are needed to get the full 3-D experience. Now projects in South Korea and Germany aim to do away with clunky frames and bring the 3-D effect to both movie and home theater viewers. An optics research team from Seoul National University has developed a glasses-free 3-D system for commercial theaters that uses space more efficiently and at a lower cost than current 3-D projection technology. The technique was reported online Aug. 20 in OSA’s open-access journal Optics Express. “There has been much progress in the last 10 years in improving the viewers’ experience with 3-D,” said Byoungho Lee, a professor of electrical engineering. “We want to take it to the next step with a method that, if validated by further research, might constitute a simple, compact and cost-effective approach to producing widely available 3-D cinema, while also eliminating the need for wearing polarizing glasses.” The key for 3-D technology lies in how polarization is handled. To produce modern 3-D effects, modern movie theaters use linearly or circularly polarized light. With this method, two projectors display similar images onto a screen, slightly offset from one another. Each projector allows only one state of polarized light to pass through its lens. When a viewer puts on polarized glasses, each eye can perceive only one offset image, adding the illusion of depth to the projected images on the screen. Actual experimental results demonstrate the promise of a glasses-free 3-D theater experience. Two cars, one red and one blue, are projected onto a screen through a parallax barrier. As the light shines back through the polarizer, two offset images are created, producing the visual cues that the brain interprets as depth. (Image: Optics Express) Because the two-projector method is bulky, optical engineers have developed multiple single-projector methods to achieve the same effect. The parallax barrier method creates the illusion of 3-D, but is also cumbersome because it requires a combination of rear-projection video and physical barriers or optics between the screen and the viewer. The obstructions are analogous to the slats in a Venetian blind, which create the 3-D effect by limiting the image each eye sees. In the new method created by the South Korean team, a “slat” effect is achieved by using different polarizers to stop the passage of light after it reflects off the screen. Next, the researchers added a specialized coating, known as a quarter-wave retarding film, to the screen to block the necessary portion of light. The film works by changing the polarization state of the projected light, ensuring that it no longer passes through the other polarizers. As the light passes back between or through the polarizers, the offset effect is created, producing the depth cues that give a convincing 3-D illusion to the viewer, without the need for those pesky glasses. The experimental setup of a proposed glasses-free 3-D theater experience is shown, with the projector in the familiar front position, creating 3-D images. (Image: Optics Express) Experimental results show that the method can be used successfully in two types of 3-D displays: The first is the parallax barrier method; the other is integral imaging, which uses a two-dimensional array of many small lenses or holes to create 3-D effects. “Our results confirm the feasibility of this approach, and we believe that this proposed method may be useful for developing the next generation of a glasses-free projection-type 3-D display for commercial theaters,” Lee said. Next, the investigators hope to expand the functionality of the method and apply it to other single-projector and frontal 3-D display methods. It may be several years before the technology makes it to your local cinema, they say. Theaters aren’t the only place viewers can reap the benefits of glasses-free 3-D technology. A new method that adapts conventional 3-D films to autostereoscopic displays in real time could make lounging on the sofa watching a 3-D movie a fun experience. Currently, 3-D movies available on Blu-ray are based on two different perspectives, one for each eye. Autostereoscopic displays, however, require five to 10 views, or even more, of the same scene to present 3-D images that can be seen from various vantage points. Now, scientists at Fraunhofer Institute for Telecommunications, Heinrich-Hertz Institute (HHI) have developed a technology that converts existing 3-D Blu-ray content in a way that enables it to be shown on autostereoscopic displays. Stereoscopic 3-D to multiview conversion pipeline. (Image: Fraunhofer Heinrich Hertz Institute) “We take the existing two images and generate a depth map — that is to say, a map that assigns a specific distance from the camera to each object,” said Christian Riechert, an HHI research fellow. “From there we compute any of several intermediate views by applying depth image-based rendering techniques. And here’s the really neat thing: The process operates on a fully automated basis, and in real time.” Previously, such depth maps could be generated only at a dramatically slower pace, and often they would require manual adaption. The real-time conversion, however, is similar to simultaneous interpretation, enabling the viewer to enjoy a 3-D Blu-ray disk glasses-free. This is possible through a hardware component that estimates the depth map in the background and generates the requisite views without the viewer even being aware of it. The team has already finished the software that converts the data. Next, it plans to collaborate with industry partners to port it onto a hardware product for integration into televisions. The group anticipates that it will be at least another year before the technology is commercially available. The technology will be displayed Aug. 31 through Sept. 5 at the IFA trade show in Berlin. For more information, visit: www.useoul.edu or www.fraunhofer.de/en