3D TV is the current hot topic. Formerly the decision faced by consumers was whether to buy 3D TV or 2D TV. Now the decision has got a whole lot more complicated as there is a further choice, when opting for 3D TV the consumer must also decide between active 3D vs passive 3D. Each variant of 3D technology have pros and cons, so there an argument can be made in favour of either. However this is just another factor that contributes to the consumer’s headache when it comes to choosing which 3D TV to buy.
Sorry if this isn’t the answer you wanted to hear but it would be wrong to declare an out right winner when it comes to the passive 3D TV vs active 3D TV debate. However what can be said is that once you know the qualities of both types of 3D TV technology you can make an informed choice dependant upon your requirements and intended use. If you read on then by the end of this article you should be in a position to make the right choice based upon your requirements and how each type of 3D TV technology fits in with this.
At this point you will find that the market is roughly divided between the two technologies, on one side you have Samsung, Sony and Panasonic pushing active Full HD 3D TV and on the other LG and Vizio are promoting the benefits of passive 3D TV.
In order to make an informed choice it helps to know some basic fundamentals of how 3D TV works, as this helps to understand the pros and cons for each type of 3D TV technology.
First, physically all TVs are two dimensional, ie they produce a flat image on the screen. In order for a two dimensional TV to produce 3D ‘effects’ it must create an illusion which fools the viewer’s brain in to interpreting the physical 2D image in front of the eyes is actually 3D. It’s not magic that does this, a 3D TV simply imitates how human eyes works. We all have two eyes, each eye views things from a slightly different angle, your brain processes these two separate images into one of depth and perspective. Simply put, what a 3D TV does is recreate these two separate images, one for each eye. A 3DTV then uses either active or passive 3D techniques to display the two images separately for the viewer’s left and right eyes. It is here where the two techniques of separating the two images intended for the left and right eyes differ, the end result is that each method produces 3D images with different characteristics on which the whole active 3D TV versus passive 3D TV debate is based.
Active 3D TV
This technique involves displaying the separate images intended for the left and right eyes alternately. Typically the 3D TV displays 120 images (frames) per second. The sequence of frames alternate between left and right, so in the case 120 frames per second this means 60 frames are displayed for each eye. The obvious question is – how are the frames separated for the left and right eyes? This is where the active shutter 3D glasses come in. The viewer wears a pair of glasses which have shutters built in to the lenses. The 3D glasses are synchronized with the TV so that the shutters alternately block the vision of each eye so that the left eye only views the left image and right eye only views the right image. Hence the ‘illusion’ is created and the brain interprets this as one 3D image.
The major benefit of this technique is that it is possible to display a full HD 1080p image for each eye making the resultant 3D images true full HD, this is why you will frequently see it advertised as ‘Full HD 3D TV’ (and the relevance of this will become apparent once passive 3D TV is explained further on). Worth noting is that there are some lower end 3D TVs that use 720p resolutions, in this instance the same theory applies each eye receives a 720p images and the end result is 720p 3D image. This fact is no different when buying a 3D TV when compared to buying a 2D TV model when ‘you get what you pay for’, if you have less to spend you may only be able to afford a TV with a smaller screen size which might be 720p and not 1080p.
As already mentioned each method has its pros and cons, so what are the disadvantages of active 3D TVs. First and foremost, as both consumers and passive 3D TV advocates alike will tell you – price. Active shutter 3D glasses are expensive, they range from $50 to $200 for a single pair. Now that might not be an issue if you only intend watching the 3D TV on your own, you will only need one pair of 3D glasses. However, if you have a wife and a bunch of kids who would love to watch 3D movies or you plan on having a group of friends over to watch a sports game in 3D whilst sinking a few beers, then it is going to be expensive to equip everyone with a pair of 3D glasses. How many pairs of 3D glasses would you need? The potential investment on active shutter 3D glasses alone should be considered before purchasing a 3D TV. Bear in mind that typically a Samsung 3D TV ships with 1-2 pairs as standard, and Sony 3D TVs and Panasonic 3D TVs don’t include any.
Technical disadvantages of active 3D TV include a reduction in brightness, motion blur and something called 3D crosstalk. Because active shutter 3D glasses are effectively blocking one half of all the frames displayed, then the perceived brightness is reduced. Motion blur happens when fast moving action is displayed, because the rate of frames per second is split between the two eyes, the effective frame rate is halved raising the possibility of blurring. 3D crosstalk is an unwanted effect when the images for the left and right eyes overlap because the active shutter 3D glasses fail to totally filter out the left image for the right eye and vice versa, the result of this is a ghosting effect of on screen images.
Final criticisms that consumers have of active 3D glasses are that they somewhat uncomfortable to wear for long periods of time both because they tend to be bulky (this situation should get better with more recent and future improved lightweight designs). Also a significant amount of users have reported that watching an active 3D TV causes fatigue, eye strain and even headaches due to the constant flickering of the active shutters.
Passive 3D TV
This method of producing 3D images still works by using a separate image for the left and right eyes. However this time rather than alternating the left and right images frame by frame, a single frame contains both the left and right images at the same time. How is this done? Every frame is made up of horizontal rows of pixels (1080 rows for full HD), alternate horizontal rows display the left and right eye images. Then through the use of a polarizing filter built in to the TV display panel, along with a pair of passive 3D glasses, the light projected from the TV is filtered out to the left and right eyes which once again the viewer’s brain interprets as a single 3D image.
The obvious disadvantage to this method is that as every frame contains the left and right images at the same time, in reality the resolution of the television is being halved (hence this is why active 3D TV is promoted as Full HD 3D TV, because each eye is displayed a full 1080p 3D image). The other disadvantage with passive 3D TV is due to a negative effect of using a polarizing filter. This method restricts the viewer to a narrow range of the vertical angle at which they can effectively view the TV. Put in simple terms,this means the viewer must be seated in a position where their eyes are close to being at the same level as the center of the TV screen. A passive 3D TV can still be viewed at a decent horizontal angle, but moving the viewing angle vertically (for example when standing up or sitting down) will reduce the 3D effects and cause unwanted horizontal lines to be visible.
However, the disadvantages as already discussed for active 3D TV do not apply with passive 3D TV. That means the brightness of images are not reduced as much because there are no shutters to block the light with passive 3D glasses, the passive filters do reduce the brightness slightly but not to the extent that active 3D glasses do. Where as the resolution is halved for passive 3D TV the frame rate is not. If a passive TV displays at 120Hz then both eyes view 120 frames per second and not 60 frames for each eye per second as with active 3D TV. The benefit of this are improved motion handling.
In relation to the passive 3D glasses themselves, they are both lightweight and inexpensive. A set of passive 3D specs can be bought for less than $10, and if you were to buy a new LG LW6500 passive 3D TV it is likely that you wouldn’t need to buy any extra pairs because it typically ships with 4-7 pairs included.
Making Your 3D TV Choice
If you base your choice of which type of 3D TV to buy on the price tag alone, then passive 3D will come out as the winner. Not only are passive 3D TVs cheaper to purchase, so are the passive 3D glasses. If you have a potentially large audience this is going to be a big factor. If your budget is only partially limited then your decision might involve a trade off between buying a larger screen passive 3D TV against buying smaller active 3D TV and couple of pairs of extra active shutter 3D glasses. When budget isn’t an issue you may decide that a big screen Active Full HD 3D TV with as many pairs of active shutter 3D glasses as your require is the choice for you.
Of course whatever your choice is, it will still come down to personal preference. Not all makes and models are as good as each other at implementing 3D regardless of the 3D technology they use. With any potentially large investment such as a 3D TV it is always wise to go down to your local TV showroom and ask for demonstration of both types of 3D TVs of the different brands and then judge for yourself whilst taking into consideration all of the pros and cons of active 3D TV vs passive 3D TV mentioned above.