3-D Display Doesn’t Disturb 2-D Viewers
SANTA CRUZ, Calif., July 22, 2013 — Watching 3-D television with stereo glasses can be cumbersome, and taking them off to give your eyes a break only leaves you staring at a blurry image. But a 3D+2D display could change that, enabling viewers with glasses to see images in 3-D, while those without them see images in standard 2-D.
With existing 3-D TV displays, viewers wearing stereoscopic glasses see a different image in each eye to get the 3-D effect. Viewers without glasses, however, see the two images superimposed, resulting in a blurry “ghosting” image.
“There are a lot of reasons why it would be desirable to not need the glasses,” said James Davis, associate professor of computer science in the Baskin School of Engineering at the University of California, Santa Cruz. “They can be expensive, so you wouldn't want to buy extra pairs, and they can interfere with other activities.”
Davis’ 3D+2D TV overcomes ghosting by showing separate left and right images when viewed through glasses, but only the left image when viewed without. The right image is obscured by displaying a third image, which is not seen through either lens of the glasses. This image is a negative of the right image — bright where the right is dark, and dark where the right image is bright — canceling out the right image so those without glasses see only the left image.
Ghosting makes a 3-D TV image (above) blurry for viewers without stereo glasses, but with 3D+2D TV (below), the image is sharp for viewers both with and without glasses. Courtesy of J. Davis.
The prototype was built by aligning a 3-D projector with a second, polarized projector used to project the negative of the right image. The image from the polarized projector is not visible through the LCD active shutter glasses synchronized to the 3-D projector.
The simple prototype enables 2-D viewers to see a low-contrast image because the darkest pixel is relatively bright. To restore acceptable contrast to non-glasses-wearing viewers, the investigators enabled the images seen by the left and right eyes of the glasses wearers to have unequal brightness, where the left becomes brighter and the right dimmer. Several experiments were conducted to determine the optimal brightness ratio between the left and right images; ratios in the range between 20 and 60 percent were acceptable for both viewers.
Experiments were also conducted to quantify the “Pulfrich effect,” which slightly distorts depth perception of moving objects when one eye sees a darker image than the other, as if the darker image had been delayed a few milliseconds. This “virtual time delay” was found to be similar to the actual time delay experienced with sequential-frame 3-D displays, which show left-right image pairs with an 8-ms delay on a 120-Hz display.
The findings indicate that the Pulfrich effect is not an obstacle to using unequal brightness; rather, it can be used to cancel the effect of the actual time delay in a sequential-frame stereo display.
A patent application has been filed, and one of Davis’ students, Jing Liu, is now working with students at Stanford University’s Graduate School of Business to start a company based on the technology.
Graduate students Steven Scher, Rajan Vaish and Prabath Gunawardane also contributed to the research.
The technology — published in the June issue of ACM Transactions on Graphics (doi: 10.1145/2487228.2487229) — will be presented July 25 at Siggraph 2013 in Anaheim.
For more information, visit: www.ucsc.edu
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