Why Do I Need To Wear Special Glasses To Watch 3D?

Man With 3D glasses
Man With 3D glasses. Getty Images - Albert Mollon - Moment Collection

As of 2017, manufacturing of 3D TVs has been discontinued. Although there were several reasons for its downfall, one of the main arguments cited for the lack of acceptance by many consumers, was the need to wear special glasses, and to add to the confusion, many consumers don't understand why glasses are needed to view 3D images.

Two Eyes - Two Separate Images

The reason that humans, with two functioning eyes, can see 3D in the natural world, is that the left and right eyes are a distance apart.

This results in each eye seeing a slightly different image of the same natural 3D object(s). When our eyes receive the reflected light that is bounced off 3D objects, it contains not only brightness and color information, but also depth cues. The eyes then send these offset images to the brain, and the brain then combines them into a single 3D image.

However, since TVs and video projectors display images on a flat surface there are no natural depth cues. In order to see the displayed images in 3D, they need to be encoded and displayed on a screen as two off-set or overlapping images.

The way 3D works with TVs and video projectors is that there are several technologies used for encoding separate left and right eye images on physical media, such as Blu-ray Disc, cable/satellite, or streaming. This encoded signal is then sent to the TV and the TV than decodes the signal and displays the left and right eye information on the TV screen.

The decoded images appear to look like two overlapping images that look slightly out of focus when viewed without 3D glasses.

As the needed left and right images reach each eye via the needed 3D glasses, a signal is sent to the brain, which combines the two images into a single image with 3D characteristics.

In other words, the 3D process actually 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, when they were offering 3D TVs (such as LG and Vizio) used a system that requires the use of Passive Polarized Glasses, while other manufacturers (such as Panasonic and Samsung) required the use of Active Shutter Glasses.

For more details on how each of these systems work, along with advantages and disadvantages of each type, refer to our companion article: All About 3D Glasses

Auto-Stereoscopic Displays

Now, some of you are probably thinking that there are technologies that enable you to see a 3D image on a TV without glasses. Such prototype and special application units do exist, usually referred to as "Auto-Stereoscopic Displays". Such displays are extremely expensive and, in most cases, you have to stand right in the center spot, so they are not good for group viewing.

However, progress is being made as no-glasses 3D is becoming available on some cellphones and portable game devices and has been demonstrated in a larger screen TV screen form factor as Toshiba, Sony, and LG first showed prototype glasses-free 56-inch 3D TVs at the in 2011 and Toshiba showed an improved model at the 2012 that was available in limited quantities in Japan and Europe.

In addition, Sharp has shown no-glasses 3D on an 8K prototype displays, and glasses-free pioneer, Stream TV Networks, displayed their production-ready glasses free 3D TV technology - so progress is definitely being made to remove the obstacle of having to wear glasses to view 3D on a TV screen.

Auto-Stereoscopic display technologies are being pursued and implemented on a limited basis (mostly in commercial, industrial, educational, medical venues where it is very practical), and although you may start to see it being offered on wider retail basis, for the most part, glasses-required 3D is still the most common method of view 3D on a TV or via a video projector.

For more on what is required to view 3D, as well as to how to setup a 3D home theater environment, refer to our companion article: Complete Guide To Watching 3D at Home.