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Passive and Active 3-D TV’s… What’s the Difference?

Posted By Randal On January 26, 2012 @ 5:36 PM In TV Tech | 2 Comments

Some time ago, I did an article here about the history of 3-D and how it was then coming to a television near you.  Now, it has come and prompting another question as it does:  What’s the difference between “active” and “passive” 3-D?  Well, I’m here to tell you.

Passive 3-d was the first 3-d format, and it still hangs around today.  In passive 3-d, two images are displayed on the screen simultaneously, and you wear glasses that can distinguish the two and blend them into a (hopefully) smooth image free of 3-d “artifacts” (the shading that you sometimes see around 3-d images).

There are two types of passive 3-d currently in use.  The first, anaglyph (red/cyan) is typically only used on standard def DVD’s.

The biggest problem with this type, since the advent of color film and TV, is that it distorts the colors on the screen.

The second type, the type used on Blu-ray discs and all modern 3-d TV’s, is polarized.  These look like sunglasses, but provide no U/V protection for your eyes, so don’t try to use them that way.

Active 3-d, like passive, uses two separate images on the screen, but this time they actually flash so fast that the naked eye can’t distinguish them as flashing.  The glasses, typically powered by batteries, contain LCD lenses that shutter in synch with the images on the screen, obscuring first one eye and then the other (again, so fast that you can’t see it), giving a flawless 3-d image.

The glasses themselves are larger and somewhat heavier than the passive polarized glasses, and require recharging between uses.  The first pairs that were used in cinemas, in fact, were so bulky and heavy that they had to be worn like baseball caps.

As a glasses wearer, I actually preferred these because they were more comfortable to wear with prescription glasses.  The biggest drawback to these, however – and the reason that theaters no longer use them – is that they gave some viewers blasting headaches, or, in some particularly unlucky cases, seizures.  Another big difference is the cost.  A passive 3-d TV can cost $500 or so less than an active 3-d TV, and you can buy four or five pairs of good passive glasses for the cost of one pair of active 3-d glasses.

Hope that this helps.

~Randal Schaffer

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