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How 3D Works


If you were just wondering – “How does a 3D TV work?“, then this guide is perfect for you.

Ever since Hollywood began it’s recent push towards 3D with animated movies such as Beowulf, Pixar’s brilliant “Up” and of course, most recently with James Cameron’s spectacular “Avatar”, many of us have begun to fall in love with the 3D movie experience. We perceive the world around us in 3D, so why should our TV watching be restricted to 2D?

While 3D technology in the past was quite primitive resulting in an underwhelming, nausea inducing experience, major consumer electronics companies are now betting on the resurgence of 3D and have been working at a furious pace to develop new technologies that can deliver a comfortable and entertaining 3D experience in the comfort of our homes.

This 3D Technology guide describes in detail how 3D tvs work and covers the pros and cons of various emerging 3D display technologies. Of course, we must first start by understanding why we perceive the world around us in 3D.

Why we perceive in 3D

The simple reason why we perceive in 3D is because we have two forward facing eyes with which we 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 key on your keyboard 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.

To take this a step further, try moving a small object close to your face and look at it with only one open eye at a time. You will notice that there is a larger shift in the position of the object for your left and right eye image when it is closer to you. If on the other hand, you place the object a few feet away from you and try the same experiment, you’ll notice that there is a very tiny shift in the position of the object in your left and right eye image. This gives you a hint at how our brain perceives depth from these visual cues.

Now that we understand why we perceive in 3D, it follows that for any display technology to be able to trick your eyes into believing that you are viewing a 3D image, it will need to provide a slightly different image for viewing to each eye via some technological trickery. Read on to learn about the different technologies being used in 3D tvs today and in the near future.

Side Note: If you want to have some cross-eyed fun and view some interesting stereoscopic images, check out the at studio3d.

Color Filter or Anaglyph Glasses

Anaglyph techniques was first developed in 1853 by Wilhelm Rollmann, a German, in Leipzig. The working is quite simple. You wear a color filter glass with each eye piece having a different color film (chromatically opposite to each other). The film or image is composed of two overlapping images in different color tints such that each eye is able to view only one of these two overlapping images. In this manner a 3D effect is achieved. However, there are a number of drawback associated with this technique, which explains why this technology has never been picked up for consumer home theater systems.

Drawbacks:

  • Due to the color tinted glasses, the image that we see has very poor color fidelity and has strong shades of red and green. While this can be mitigated to a small extent by using different color pair glasses (red-cyan) it is still a significant drawback.
  • The quality of the 3D image in general is quite poor resulting in a feeling of nausea and a forgettable viewing experience.

 

Advantages:

  • Cheap – The glasses themselves cost less than a dollar. In addition, any digital HDTV or LCD monitor is capable of displaying the necessary color tinted 3D video. While this is an advantage, on the whole the drawbacks far outweigh this single advantage
  • 3d Polarized Glasses were used in the 1952 for the screening of Bwana Devil - Thanks to Ron@studio3d.com for the correction

 

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. Both the IMAX 3D and RealD rely on utilizing the unique properties of polarized light to create a drastically improved 3D viewing experience.

Polarization of light is defined as the plane along which the electric field of the light oscillates. I just threw that in in case you care enough about the definition . While it isn’t necessary to understand the details, polarization of light enables the ability to selectively screen out light based on its polarization by using unique materials called polarizing films. As illustrated in the image below, a projector is used to project two skewed images on a special screen that allows the reflecting light to retain its polarization (the screens are usually coated with silver to achieve this). Each image is projected with a polarization mutually orthogonal (90 degrees) to the other polarization. The Polarizing glasses consist of two polarizing films that allow light of different polarizations through. As a result, as illustrated below, one eyepiece allows one image through, while the other eyepiece allows the other image through due to the differing polarizations of the incoming light.

How polarized glasses work - Credit Howstuffworks.com

The end result is that each eye perceives a different image and as explained earlier, this results in the 3D effect. In reality, commercial systems like RealD actually use a special type of polarized light called circularly polarized light. The 2 images are either right-circularly polarized or left-circularly polarized. The advantage of using circularly polarized light is that you can tilt your head from side to side without affecting the contrast and brightness of the image you view.

If you’re wondering whether the polarized glasses you brought home with you from the movie theater will work with a new 3D tv that you plan on purchasing, the chances are that it won’t. The reason for that is that most consumer electronics companies are betting on a different technology for first generation 3d televisions (see the next section). The good news is that LG has said that it is currently developing a 3D ready tv based on this polarized light technology.

Advantages:

  • One of the best 3D viewing experiences amongst current technology with rich colors and great detail
  • Glasses are passive (not electronic) and as a result very cheap.
  • Easy to switch between displaying 2D and 3D content

 

Drawback:

  • The only major drawback at the moment is that this technology is not being widely adopted by electronics makers for the first generation of 3d tvs.

 Active Shutter Glasses

Active shutter display technology is the primary technology that is being championed by a number of big name manufacturers such as Sony, Panasonic and Nvidia. In this method, the left and right images are displayed alternatively ina sequential manner on a regular LCD TV. However, since the effective frame rate is halved, these displays need to have double the refresh rate of standard LCD monitors and TVs (60 Hz). This is why you will find that all 3D ready TVs have a minimum frame rate of 120 Hz. Shutter glasses are used to discriminate between the images so that each eye only sees the corresponding image on the monitor.

Panasonic's Active Shutter 3D Glasses

Each eyepiece of the special active shutter glass acts as a shutter and the left and right eye pieces are shuttered alternatingly 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. These special glasses usually contain liquid crystals that can be made opaque thus acting as a shutter. Thus, using the active shutter technology, the left eye only sees the intended left view image and the right eye sees the intended right view image.

The first generation Active Shutter TVs and displays are already in production and should be rolling out any time now. Nvidia already sells active shutter kits for 3D gaming. Newer models are also specd with 240Hz refresh rates that should help with smoother 3D video and less flickering. This improved refresh rate should have a notable effect when it comes to fast moving scenes and sports viewings.

Advantages:

  • Robust, mature technology that has already demoed at CES 2010 with Sony and Panasonic backing it.
  • Reduced eye fatigue

 Drawbacks:

  • Glasses are expensive and require batteries. It would suck to run out of batteries mid-way through a movie watching. Expensive glasses also make it prohibitive to have a bunch of friends over to watch the Super Bowl in 3D
  • The videos can be dim as the glasses reduce the brightness of the image. In addition, 120 Hz can be too low a refresh rate for fast moving sports and movie scenes. This can result in choppiness and flicker. 240 Hz displays should go a long way in fixing these issues.


3D TVs without glasses

Watching 3D video without the inconvenience of feeling like dorks wearing sunglasses inside your own house is really the holy grail when it comes to 3D technology. Fortunately there is some exciting news on that front. This technique is called autostereoscopy and surprisingly, it has been around for a long time. Autostereoscopy relies on 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. This can typically be achieved in flat panel displays either using lenticular lenses or parallax barriers. The image below is an example of a lenticular lensed flat panel. The unique grooved shape of the surface allows the projection of different images based on viewing angle thus enabling stereoscopic vision.

Lenticular lenses for glass less 3D TVs

However, eye strain and headaches are usual side effects of long viewing exposure to autostereoscopic displays that use lenticular lens or parallax barriers. Such displays can have multiple viewing zones allowing multiple users to view the image at the same time. LG has recently announced a 3D TV codenamed M4200D that uses such a lenticular lensed system. One caveat of this system however is that there is an optimal viewing distance that is quite rigid (approximately 13 feet). If you sit further away or too close to the TV, the quality of the 3D image can degrade significantly.

Similar to the lenticular lens technology, parallax barriers, pioneered by Sharp, also enable 3D TVs without the need for bulky glasses. This technology relies on a parallax barrier comprising of switchable liquid crystals that can be tuned by applying a potential so as to control the direction in which light is transmitted through the LCD panel. As a result, but controlling the direction of light transmission, the image viewed by the left and right eye can be independently modulated so as to generate as 3D effect. A significant advantage of this technique is that the switchable liquid crystal barrier can be turned off so as to enable the display of regular 2D content.

Unfortunately the glass less 3D TVs are still in a prototype phase and aren’t yet ready for full scale production. However, with the current thrust in the area of 3D TVs, and if there is wide spread adoption of 3D TVs over the next 5 years, then these glass less 3D TVs will definitely make the transition from proof of concepts to robust, commercial, mass-produced products.

Advantages:

  • No need to wear dorky glasses! Easy transition between watching 2D and 3D content.

 Drawbacks:

  • While the glass less aspect is appealing, the rigid requirement on optimal viewing position makes it a little less exciting. People will need to design their living rooms around their TVs more than ever if these TVs get widely adopted.

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