Active or Passive? Its a walk-over!


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With the forthcoming Olympics being broadcast in 3D free-to-air, there is sure to be a surge in new TV purchases. Given so many 3D capable models to choose from, which is best?
Until the manufacturers come out with autostereoscopic designs that work properly in high definition, we have to view 3D though some sort of glasses to separate the left and right images when viewing a 3D TV set. For home entertainment, there are only two main choices: active or passive glasses.

Active 3D glasses use an electronically sequenced shutter to alternately blink each eye in synchronism with the display showing left and right images in quick succession. This is possible because plasma and modern LCD panels are capable of very fast switching so can create left and right images within the timespan of a single television frame.
It costs the manufacturer little more to make a 3D-ready set than a 2D model with 100/120 Hz refresh. The down side is that the active glasses are expensive because they need two high-speed LCD shutters, the associated drive electronics and some kind of wireless receiver for the sync signal, plus a battery. They are also relatively bulky.
With passive 3D glasses system, the extra cost arises in the LCD panel manufacture. (This technology is not suitable for plasma panels). In a 3D LCD, the screen polariser has a layer of alternating strips of left and right handed filters that are accurately line-up with the display line structure. Viewed in 2D with no glasses, this makes no difference to the viewer. Passive 3D glasses have low-cost left and right hand polarisers that filter out the images which are vertically separated by the TV’s display filters. So here the set is more costly and specialised to make but the glasses cost almost nothing compared with the £50 to £100 per pair charged for active types.
This is why new 3D active sets come with one or two pairs in the box. With passive glasses, you might get 10! But technically which is best? Active shutter systems give the full vertical resolution and you do have a choice of plasma as well as LCD technologies. However, modern LCDs are just as good as plasma and the loss of vertical resolution with passive glasses is not really apparent in normal viewing conditions. Motion portrayal can be noticeably better with passive glasses. Then there is question of brightness. With both systems each eye is only seeing roughly half image and through a light reducing filter. So both are about the same or slightly less for shuttered. Some people report that flicker is annoyingly visible with active glasses.
When you add in the cost of three or more spare sets of active glasses to the price of the set, an active model is more expensive. If you want the cheapest initial purchase, if you have no friends or family, if you are never going to lose or break your active glasses, if you don't mind the batteries going flat, and if you are not going to take them round to a friend's house and expect them to work there too, then go for an active system.
However if you want to share the 3D viewing experience with visitors and not worry if they walk off with or sit on your £1 glasses, then go for a passive 3D TV set. Perhaps LG.


Robin Palmer is Managing Director of Cel-Soft and is currently involved with software solutions for 3D & TV quality control and measurement technology.

Tags: iss061 | 3d glasses | active 3d glasses | passive 3d glasses | N/A
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