By Chris Boylan
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At the year’s Consumer Electronics Show and in the weeks that have followed, a line in the sand has been drawn around two different approaches to 3D TV. In one camp, we have Panasonic, Samsung and Sony, touting the benefits of Full HD 3D TV with their active 3D glasses that deliver full high definition (1080p) images to each eye. In the other we have VIZIO and LG waxing poetic on the benefits of a passive 3D TV solution which, though it may sacrifice detail, offers other benefits such as less flicker and lighter, less expensive 3D glasses. Which is better? This is not a simple question to answer. But which technology is a better choice for the consumer depends on preferences and intended use for 3D in the home. To make an informed decision, it is helpful to understand how both technologies work.
It’s All an Illusion
With either the passive or active approach to 3D TV, the intent is to fool your brain into thinking it is seeing a three dimensional image from a two dimensional screen. The way this is done is based on the concept of stereoscopy: because our eyes are positioned a few inches apart, we see a slightly different image with our left eye and with our right, and this difference is interpreted by our brain as depth. If an image is far away, the left and right eye images are pretty similar, but if it is close, the left and right eye images are quite different. If you can present the left and right eye with each “half” of a stereoscopic image, then our brains will see the illusion of depth. But how you get there with active vs. passive technology is a bit different.
Details R Us
With active 3D, you have a TV that delivers images at 120 frames per second, alternating between a left eye image and a right eye image. An active 3D TV set uses the full resolution of the imaging system (LCD panel, plasma panel or a projector’s imaging engine) for each eye, which is typically full high definition 1080p: 1920 pixels wide by 1080 pixels high. There are some lower resolution active solutions such as 3D-capable 720p plasma panels and 720p DLP projectors, but we’ll ignore these for now.
Because the active panel presents both the left eye and right eye images on screen in rapid succession, the naked eye sees a blurry image with no 3D effect. However, if you put on a pair of active shutter 3D glasses, the glasses synchronize themselves to the 3D TV, allowing your left eye to see only the left eye frame, and the right eye to see only the right eye frame. The glasses employ an electronic shutter system that blacks out the left eye image when the right eye image is on screen, and vice versa. Your brain then processes these discrete left eye/right eye images as 3D to form the illusion of depth.
The benefits to active 3D are that you can see the full detail of the image in both eyes. This presents a realistic and high quality 3D effect for most viewers. The drawbacks are that these active 3D glasses are fairly expensive to manufacturer, hence more expensive for the consumer – typically selling from $100 to $200 per pair. Want to have a 3D movie night or Super Bowl party for your friends? Expect to spend as much on the glasses as you did on the TV, if not more. The additional drawback of active 3D is that the electronics in the glasses tend to make them rather bulky and heavy, which can lead to discomfort over extended viewing periods. Manufacturers are working to improve this however, with Samsung’s newest active shutter 3D glasses weighing in at under one ounce.
Bring the Movie Theater Home
Passive 3D TVs work a little bit differently, more like 3D movie theaters. A passive 3D TV uses a technique call circular polarization to create discrete left and right eye images by polarizing the left and right eye image’s light output in different directions. Again, as with active 3D, a passive 3D TV in 3D mode will look blurry to the naked eye, as you are seeing the left and right eye images on screen at the same time. But a pair of passive 3D glasses will filter the light properly so that the left and right eyes will see their respective images and your brain will create a 3D image from the result. Those same light 3D glasses you get at most 3D theaters will work with most passive 3D TVs.
With passive 3D projection systems, you can still get the full resolution of the projector on screen for each eye, but you actually need a separate projection engine – a separate projector with its own lens – for the left and right eyes, which can get expensive and can be tricky to align precisely. Some 3D projectors actually include dual projection engines and lenses into a single chassis, an elegant, though normally expensive, solution.
With flat panel 3D TVs, the way the passive 3D technique is accomplished is via a polarizing filter built into the screen. These filters polarize each alternating line of the image for the left and right eyes. The drawback here is that you are then splitting the panel’s resolution or detail in half by allocating half of the pixels to the left eye and half to the right eye. This is compounded when you view a side-by-side (SBS) 3D source as these images have already lost half their detail in transmission so you effectively end up with 1/4 of the full resolution.
Also, the vertical range or viewing axis of a passive 3D TV system tends to be much more restrictive than an active system. If you try to watch it from too low or too high, the 3D effect collapses and you will see a doubled image. On the other hand, horizontal viewing axis of a passive 3D system is fairly wide so it can be a good choice for “event viewing,” e.g., watching a 3D sporting event in a sports bar. One benefit of a passive 3D system is that the light transmission tends to be higher, leading to a brighter image compared to active 3D. Another benefit is that the passive 3D glasses can be much less expensive, lighter and more comfortable as they contain no active shutter system or electronic processing.
An additional advantage of passive 3D systems is that, instead of being limited to a refresh rate of 120 Hz (120 frames per second), with the left and right eye seeing images at 60 Hz each, a passive 3D TV can be run at 240 Hz or more, enjoying the benefits of reduced blur and improved motion resolution even in 3D mode. Passive 3D sets can also potentially employ native cinema modes for movies (a display rate that is a multiple of a film’s 24 frame/second rate) which can present a more film-like image to the viewer, free from an effect known as “judder” where motion can be jerky and uneven and free from artificial-looking motion smoothing techniques that can make movies look more like video. Active sets could be enhanced for these feaures in the future, but currently all active 3D TVs available in the U.S. are based around a 120 Hz (60 Hz to each eye) delivery system when in 3D mode.
Manufacturers Weigh In
Panasonic, a strong proponent of active 3D technology, began showing their full HD 3D TV solution as early as 2008 at the CEATEC show in Japan, and introduced the first full HD 3D TVs to the public in March of last year. When we spoke with their CTO Eisuke Tsuyuzaki at CES, he told us he was disappointed that some manufacturers were switching to a passive solution as it represented a “large step down in picture quality, which is bad for the customer, and bad for the 3D TV market.” Apparently Sony and Samsung agree as they too remain committed to active 3D TV solutions.
Meanwhile LG’s Tim Alessi, director of new product development for LG Electronics says that their own private market research has shown that consumers prefer a passive 3D TV solution 3:1 after seeing both types in action. At LG’s Cinema 3D launch event last month, Tim told us, “We intend to release both active and passive 3D TV systems this year, but in 2012, we expect to offer only the Cinema 3D (passive) models.” VIZIO will be following the same path but more aggressively as they are not releasing any new active 3D TV models this year, focusing instead only on passive 3D TV solutions.
Format War or Consumer Choice?
Although we see this passive vs. active 3D TV division as a kind of format war, the fact is that both approaches to 3D are valid, and neither truly excludes the other. The sources that work best with 3D TV today, namely Blu-ray 3D players and 3D-capable cable and satellite set-top boxes, work equally well with either system. And the 3D movies you may buy or rent on Blu-ray 3D Disc or on streaming services such as VUDU also work with either system.
So if you’re in the market for a 3D-enabled TV, your best bet would be to take a look at both types, read the reviews and decide which format is best for you: do you need the highest possible detail or do you want the flexibility of using inexpensive passive 3D glasses? The good news is that both types of 3D TVs also work perfectly well in 2D mode at full resolution. So for the vast majority of content that is not yet available in 3D, you’ll get to see every last detail without having to wear any glasses.
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