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3D - How Does It Work?

3D is based on the principle of stereoscopy, which creates the illusion of depth in an image. The easiest way to enhance depth perception in the brain is to provide the eyes of the viewer with two different images, representing two perspectives of the same object, with a minor deviation exactly equal to the perspectives that both eyes naturally receive in binocular vision.

There are currently three kinds of 3D technology on the market and each one works differently:

The first one, anaglyph technology, is the most famous one (think red/blue paper glasses) but usually the 3D effects are not so great.

The second one, polarized (or passive) technology, is the technology you have been exposed to when watching a 3D movie in an IMAX theater (e.g. Avatar 3D, Alice in Wonderland 3D, etc.). Now some brands are using this Technology in new 3D HDTVs as well.

The third one, active technology, is the most recent technology that was used in all the first generation of 3D HDTVs that came out in 2010. This is still a popular approach to 3D HDTV and despite the introduction of passive 3D technology in HDTVs this year, active technology is still the only approach used by a number of the biggest TV brands.

Anaglyph Technology:

Is 3D new? Not at all.

For the longest time, mankind has been interested in creating a 3D effect on a 2D screen. Most painters created some effect of perspective in their paintings to simulate a 3D effect.

More recently, in 1853 Wilhelm Rollmann developed a technique to simulate 3D. He created anaglyph images using two color layers superimposed but offset with respect to each other to produce a depth effect. Usually the main subject remained centered while the foreground and background shifted laterally in opposite directions. When viewed with two-color glasses (the lenses are chromatically opposite in color usually red and cyan), these images produced a stereoscopic 3D effect (your brain is tricked into thinking that this picture is in 3D).

This technology has been used countless times in movie theaters, as the typical red and blue glasses are inexpensive. The movie Bwana Devil is regarded as the first of the commercial 3D movies in the 1950s. However, while the 3D effect were fun to watch, the pictures were of low quality and had strong shades of green and red.

Polarized (or Passive) Technology:

This is where it gets interesting. Most of us have seen Avatar or other movies in IMAX 3D with polarized 3D glasses. These glasses create the illusion of three-dimensional images by restricting the light that reaches each eye, creating a stereoscopic, or 3D, effect. This technology is now available in HDTVs and is often referred to as Passive 3D. LG calls their version of it Cinema 3D, and Vizio is calling it Theater 3D -- but it’s the same underlying concept.

To create that 3D effect, two images are projected onto the same screen through different polarizing filters. The viewer wears low-cost eyeglasses which also contain a pair of different polarizing filters. Through the filters, each eye sees a different picture (each filter allows the light which is similarly polarized and blocks the light polarized in the opposite direction). This is used to produce a three-dimensional effect by projecting the same scene into both eyes, but depicted from slightly different perspectives.

The Upside
The great thing about this technology is that the glasses you need to wear to enjoy 3D are really inexpensive compared to the high cost per pair of active shutter glasses needed for Active 3D TVs. The result is that you can actually afford a pair of glasses for everyone in your family and a few friends to watch a 3D movie together. Another advantage is that the passive approach does not cause the flicker effect that can be noticeable on Active 3D HDTVs at lower refresh rates. Both of these benefits combine to allow for 3D HDTV at a lower cost than Active systems can usually be had for.

The Downside
Sounds great why not just go for passive? Here’s where things get a little technical: because a passive system is taking one HD image and splitting it in two, the result is that from an original 1080P image, each eye is only seeing a 540p image, so essentially, you’re ending up with half the combined resolution that an active system offers. So here you have a cool new 1080P HDTV, you bought a blu-ray player so you can get awesome picture quality, and you’ve cut all this resolution in half to got the 3D effect. Many people feel this results in less detailed images and a less pronounced 3D effect than most active systems offer.

Active Technology:

This technology has been adopted by most consumer electronics firms, including LG, Samsung, Panasonic, and more. With this technology, an HDTV will display one image to your left eye and one image to your right eye. Since the effective frame rate is halved, these HDTVs need to have double the refresh rate of HDTVs (60 Hz). This is why you will find that all Active 3D HDTVs have a minimum frame rate of 120 Hz (most have a frame rate around 240 Hz or even 480 Hz).

Active liquid crystal shutter glasses are then worn by the viewer and quickly block each eye in sequence to ensure that each eye only sees the corresponding image being displayed on the 3D TV set. The active shutter glasses are kept in sync with the HDTV using Bluetooth, infrared, or radio technology. These special glasses usually contain liquid crystals that can be made opaque, thus acting as a shutter. These glasses are battery-operated (battery life estimated at around 80 hours or so).

The Upside
Right now, an active 3D HDTV using Liquid Crystal Shutter Glasses is the only way to get a full 1080p image in 3D to each of your eyes. The higher image quality also appears to most people to result in a more pronounced 3D effect. If you want the highest quality 3D viewing experience, active is definitely the way to go.

The Downside
The downside for Active 3D is cost. Because active systems need to have higer refresh rates to avoid a flicker effect the HDTVs using this technology can end up being a bit more expensive than a passive 3D HDTV. The biggest real cost difference though is in the glasses. Active glasses are a much more complicated technology, and they typically sell for over $100 a pair. What if you have a big family, or a lot friends and you all want to watch 3D movies or live sporting events together? At that point, you need to buy these expensive glasses for each person who wants to watch.

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