Researchers at the University of California Santa Cruz have developed a 3D display which can also be viewed in 2D without glasses, and without the blurred effect caused by overlapping images. Though, as you'd expect, the screen displays both left and right images, it also emits a mysterious third image which is the key to the technology.

Regardless of whether active or passive 3D technology is at work, glasses-based 3D televisions rely on those glasses to selectively show each eye one of two pictures displayed on the screen. Because the two images are shot from slightly different perspectives (mimicking the slightly different views we'd see with each eye), our brain is able to put the two images together, creating the three-dimensional effect. But without glasses, both eyes see both pictures at once, creating the blurred effect that renders glasses-based 3D pictures all but unwatchable without the appropriate eyewear.

Not so UCSC's new technology, which cleverly uses a third image which remains apparently unseen to viewers, whether or not they're wearing 3D specs. Viewers without glasses will only see the left image because the right is cancelled out by the third, which is an exact negative of the right. 3D glasses mask the third image altogether.

The technology isn't perfect because it compromises the available contrast to 2D viewers and so, as a compromise, the researchers show 3D viewers a dimmer image to the right eye and a brighter image to the left. According to a UCSC press release, the researchers found that brightness ratios between 20 and 60 percent were "acceptable" to viewers of both 2D and 3D pictures.

The researchers' prototype was "built" using an ordinary 3D projector, with the negative image overlaid using a separate 2D projector. The researchers used active 3D glasses, in which shutters in the left and right eye open and close in sync with the on-screen images, creating the 3D effect. The synchronization additionally meant that the the 2D negative of the right image remained unseen by glasses wearers.

UCSC student Jing Liu is looking into the possibility of commercializing the technology.