Two Eyes, Two Images
The reason why humans, with two functioning eyes, see 3D in the natural world is because the left and right eyes each have their own perspective, separated by an inch or two. The tiny distance between the eyes subtly offsets objects within the field of view, providing dimensionality. When our eyes receive reflected light bouncing off objects, the light contains not only brightness and color information but also depth cues. The eyes send the offset images to the brain, which combines them into a single 3D image. This enables us to not only see the correct shape and texture of objects, but also allows us to determine the distance between objects within a space. Since TVs and video projectors display images on a flat surface there are no natural depth cues that allow us to see texture and distance correctly. The depth we think we see is derived from the memory of how we have seen similar objects placed in a real setting, along with other possible factors.
How 3D Works with TVs, Video Projectors, and Glasses
To see images displayed on a flat screen in 3D, they need to be encoded and displayed on the screen as two off-set or overlapping images, which are then recombined into a single 3D image. 3D TVs and projectors work by encoding separate left and right eye images onto physical media. The encoded signal is sent to the TV and the TV decodes the signal, displaying the left and right eye information on the screen. The decoded images appear as two overlapping images that look slightly out of focus when viewed without 3D glasses. Through 3D glasses, however, the left eye lens receives one image, while the right eye lens receives the other. As the left and right images reach each eye via the 3D glasses, a signal is sent to the brain, which combines the two images into a single image with 3D characteristics. The 3D process fools your brain into thinking it is seeing a real 3D image. Depending on how a TV decodes and displays the 3D image, a specific type of glasses must be used to see the 3D image correctly. Some manufacturers made use of Passive Polarized Glasses, while others manufacturers required Active Shutter Glasses.
Auto-Stereoscopic Displays
There are technologies that allow you to see a 3D image on a TV without glasses. Usually referred to as “Auto-Stereoscopic Displays,” these high-tech screens are used primarily in commercial, industrial, educational, and medical settings. They are very expensive and, in most cases, you have to view from or near the center spot, which means they’re not great for group viewing. No-glasses 3D has been available on some smartphones and portable game devices. Toshiba, Sony, and LG first showed off prototype glasses-free 56-inch 3D TVs in 2011. Toshiba showed an improved model in 2012 that was available in limited quantities in Japan and Europe, but has since been discontinued. Sharp and Samsung have revealed no-glasses 3D tech on several 8K prototype displays, and Stream TV Networks is on the forefront of bringing glasses-free TVs to the commercial and gaming space. A huge 3D advocate, James Cameron is pushing research that could make glasses-free 3D available for movie theaters in time for one or more of his forthcoming Avatar sequels. Auto-Stereoscopic display technologies have thus far been implemented in a few professional or industrial settings, but you may start to see it offered in consumer devices. Production cost and demand will be determining factors with regards to future availability. Until then, the use of 3D glasses will be the most common way of viewing 3D content on a TV or video projector. Although new 3D TVs are no longer available, this viewing option is still available on many video projectors.
