Delegates at the NAB Convention in the USA have been analysing the road ahead for 3D-TV television displays.


Active shutter glasses


The first commercial 3D-TV displays available to the public used ‘active shutter glasses’. One picture is displayed after another. First displayed is the left eye image, then the right eye image, and so on. Shutter glasses, controlled by an infra-red signal, ensure the correct eye sees the correct Image. One of the drawbacks is that the left and right eye images are not taken to the brain at exactly the same instant. For various reasons, which are similar to what scientists call the ‘Pulfricht effect’, this means that there will be errors in the depths of objects in the scene. On the plus side, there is a relatively clean switch between right and left images, with no smearing over to the next image (lag).



Passive glasses


The other approach used today for commercialy available 3D-TV sets is to display the left and right eye images at the same time, but on alternate lines of the same picture. Alternate lines are given different polarisations (the light emitted has different directional properties). The viewer has ‘passive glasses’, the lenses of which respond to the different polarisations, so that each eye sees the correct image. In this case there are no depth errors, but the vertical resolution of the image has been halved by the process, and there can be more smearing over of one image to the next than for the first method



The future of 3DTV displays


A difficult choice? Each of the two ways of displaying 3D-TV have their advocates, with a slight majority claiming the second approach has more future. One thing everyone agreed on was that making large 3D-TV displays that do not need glasses, and can be comfortably viewed by a number of people at the same time, is still quite some way away, perhaps as much as ten years.

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