Active 3D Glasses vs Passive 3D Glasses

S3D (Stereo 3D) programming is made to work with one of two kinds of glasses - active or passive (polarized or anaglyph).

Passive glasses

Strictly, any 3D glasses that do not require power are termed 'passive'. In practice, Polarized 3D Glasses are the only passive glasses that provide the quality demanded by the modern consumer or movie viewer. While anaglyph glasses with different colour lenses are still often associated with 3D movies, the colour shifts or losses inherent in the approach make them a rare sight today.

There are two sorts of Polarized 3D glasses - circular polarized and linear polarized. Circular polarized glasses have one great advantage over linear polarized glasses, in not requiring the viewer to keep their head upright to maintain the 3D effect. So circular polarized glasses are a more comfortable experience for wearing during a long movie or TV programme.

In the cinema, polarized glasses require a special silver screen that preserves the polarization, although Dolby have developed a technology that allows passive glasses to work with a standard screen. The system uses slightly different RGB spectral components in the L and R signals, and the glasses select the right components for the correct eye.

As there is no need for a power source or complex powered lenses, Passive 3D Glasses are usually considerably cheaper than Active 3D glasses.

Active glasses

Active (Shutter) 3D glasses are the most common type used in the home. Based on LCD lenses, which can be controlled to stay clear or become dark (open and close) alternately, a power supply operates the optics, while a synchronizing mechanism ensures the viewer sees the right images at the right time.

While earlier glasses needed to be connected to the TV by a wire, an infrared beam similar to that used by remote controls now sends the signal. Batteries contained in the glasses supply the required power.

But the major drawback with active glasses is higher price, owing to their complexity.

Passive or Active?

Neither type of 3D glasses is perfect. Indeed, using glasses at all is a weakness of current 3D viewing methods. But at home, Active 3D Glasses usually give the best results as they deliver images that aren't tampered with - containing full colour and picture information, unlike passive glasses which reduce the picture resolution slightly. At home, the best 3D through Active Glasses is a great, immersive experience, so effective that most people soon forget they are wearing them. But at the cinema, neither active nor passive glasses give a superior experience. It's all great!

David Throup is R&D Group Leader at Quantel. The company develops innovative, world-leading content creation systems for broadcast, post and DI. Quantel products deliver at SD, HD, 2K, 4K and 3D Stereo.

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