3D definition – the facts

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3D broadcast TV began in October last year, shortly following the advent of 3D hardware in the shape of TV sets and Blu-ray players. Initially there were few 3D discs available, but now the floodgates have opened – not only for the discs but in the cinema: 3D entertainment has become all the rage, at least amongst those who produce it. Not all 3D pictures are equal, however, especially those viewed at home.

Broadcast versus local disc

3D broadcasts are available from Sky and cable company Virgin. Each has at present a single TV channel devoted to them, offering a wide variety of programming. While ordinary HD set-top boxes are compatible with 3D programmes it’s essential, of course, to have a 3D-capable TV set, connected via an HDMI link; viewing spectacles; and a subscription to be able to view them. Because of their limited bandwidth/bit-rate these broadcast sources can deliver a maximum image resolution of 960×1080i in a format which can in effect transmit two pictures simultaneously within the same frame period as a single 2D picture.

Blu-ray discs have a sufficiently large storage capacity and data delivery rate to embrace 1920×1080p 3D images, a great improvement on broadcast pictures. This capacity is only realised if the original material was shot at this level of detail, and no processing has impaired it. It’s not possible to convert or update existing 2D players to give 3D playback, though a 2D player can produce 2D images from a 3D disc, while the price premium for a 3D Blu-ray player is not very great – which is more than can be said for 3D TV sets at present.

Active versus passive spectacles

Of the two alternative screen/spectacle systems, the simpler passive one works with a relatively expensive screen which simultaneously presents the left and right eye images in light-polarised form. The matching viewing glasses have oppositely-polarised lenses, blocking the ‘wrong’ image for each eye. This works fine, gives little viewing stress, but here there needs to be a complete set of pixels on the screen for each eye, halving the available definition of the display panel. This forms a reasonable match to broadcast and cable-derived 3D pictures, but impairs off-disc ones.

The more common active viewing system presents the full pixel-count (1920×1080 on a big screen) to each eye by means of a sequential delivery. Here the left and right eye images are shown alternately at a fast rate, while an infra-red emitter sends pulses to the viewing spectacles to synchronise their LCD lenses, blacking out the wrong image for each eye in turn. With their inbuilt electronics and fast liquid-crystal shutters these are much more expensive than passive types (which can cost pennies), while the matching display screen is less complex. Active displays can cope with the full definition of which Blu-ray is capable.


I have no doubt that in the fullness of time all mainstream TV sets will, like the existing Sony model KDL40-HX803, incorporate the 3D decoding and screen-switching electronics (relatively cheap in mass production) in 3D-ready form, leaving the buyer to upgrade to 3D at the time of purchase or any time in the future by purchasing the retro-fit IR emitter and as many pairs of viewing spectacles as required, at about £50 and £100 respectively. This is attractive to customers who want to future-proof their new purchase without the initial commitment and expense of a full-blown 3D outfit.

The ultimate 3D screen would not require any viewing glasses at all. Physically-complex designs can achieve this, but not yet in large ones with wide viewing angles at any reasonable cost. There would be a huge market for no-glasses 3D screens.

A plea

On another subject altogether, I really would appreciate any feedback from readers of this column, which I’ve now been writing for over 18 years. Any comments or constructive criticism – good or bad – would be welcome, along with suggestions for coverage in future issues, and whether you best like details of leading-edge technology, repair-bench stuff, reminiscence or whatever. You can reach me via the magazine (details on page 3) or direct at barrystreet19@yahoo.com. I promise to personally answer every e-mail. Bring it on… n

Please send your feedback to Barry Street at barrystreet@yahoo.com or to IER editor Anna Ryland at aryland@datateam.co.uk

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