How 3D televisions work

HOW 3D TELEVISIONS WORK

Why we perceive in 3D

The simple reason why we perceive in 3D is because we have two forward facing eyes working together as a team to observe the world around us (binocular vision). Our eyes are separated from each other by about 3 inches. As a result, one eye perceives a slightly different image than the other eye. For example, if you look at a word on this page with only your left eye open, and then your right eye, you will see pretty much the same image, except that each eye gives you a slightly shifted perspective of the same object. This is referred to as parallax and is crucial in our ability to perceive depth. The human brain is wired such that when it simultaneously receives images from the left and right eye each possessing a slightly shifted perspective, it is able to combine these images such that we are able to perceive the depth or distance of an object (stereopsis or stereoscopic vision). 

In order for us to perceive a 3D image on a flat surface such as a television, it needs to utilize some form of technology that provides a slightly different image for viewing to each eye.  Let’s explore those options below.  As an interesting side note, approximately ten percent of people are unable to appreciate this 3D imagery, most commonly due to strabismus (crossed eyes that don’t work together as a team) or amblyopia (a lazy eye that sees very poorly).

Polarized Glasses

Polarized glasses are the technology of choice when it comes to commercial 3D projectors that are used in 3D movie theaters around the world. Polarization of light is a unique property that enables us to selectively screen out light using materials called polarizing films. 

Two overlapping but slightly skewed images with different polarization are projected on a special screen.  The polarizing glasses worn by the viewer consist of two polarizing films that allow light of different polarizations through. As a result, one eyepiece allows one image through, while the other eyepiece allows the other image through due to the differing polarizations of the incoming light.  The end result is that each eye perceives a different image and as explained earlier, this results in the brain perceiving a 3D effect.

This technology provides one of the best 3D viewing experiences with rich colors and great detail, and the glasses required are inexpensive.  Unfortunately, the polarized glasses you brought home with you from the movie theater likely won’t work with the new 3D television that you plan on purchasing, because most consumer electronics companies are using a different technology for their first generation models.

Active Shutter Glasses

Active shutter display technology is the primary technology that is being utilized by a number of the big name electronic manufacturers. In this method, the left and right images are displayed alternatively in a sequential manner on a regular LCD TV, and “shutter glasses” are used to discriminate between the images.  These special glasses alternately shut off the left eye and right eye in a synchronized manner so that each eye only sees the corresponding image being displayed on the 3D TV set. The active shutter glasses are maintained in sync with the television set using bluetooth, infrared or radio technology. The main drawback to this technology is that the shutter glasses are expensive and require batteries.  A screen with high refresh rate is required for a smooth view of fast moving sports and movie scenes.

3D TVs without glasses

This is considered the holy grail when it comes to 3D technology, and involves the use of special optical elements between the television screen and the viewer so that each eye of the viewer receives a different image thus producing the illusion of depth (“autostereoscopy”). This can typically be achieved in flat panel displays either using lenticular lenses or parallax barriers.

A lenticular lens is an array of magnifying lenses, designed so that when viewed from slightly different angles, different parts of the underlying image are magnified.  This unique grooved shape on the surface of the television allows a different view to be projected to each eye, thus causing a 3D image.  A parallax barrier consists of a layer of material with a series of precision slits, which controls the direction in which light is transmitted through the LCD panel.  This allows each eye to see a different set of pixels, generating the three dimensional effect.  One advantage of this technology is that using a switchable liquid crystal barrier allows it to be turned off so that the television can also display regular 2D content.

The major disadvantages are an effective reduction in screen resolution, and that there is an optimal viewing distance or position for these screens (the quality of the 3D image can degrade significantly if outside this “sweet spot”).  Autostereoscopic technology is still mostly in the prototype and commercial market phase, but if the demand for 3D technology continues to grow and improve, these televisions will likely become mass-produced consumer products.