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Going 3D? The Difference Between ‘Passive’ And ‘Active’

3D GlassesIf you’ve been looking into upgrading your home cinema setup to take advantage of 3D, you may have noticed that prefixes such as Active and Passive have been cropping up on product specifications. If you’re stuck between choosing two televisions, each with a different type of 3D, yet both boasting different credentials about why their 3D is the best, you may have asked yourself: “what’s the difference?” and, perhaps more importantly before you spend out, “which is best?”

For 3D to work, either in the cinema or at home, each eye has to see different information from the same image in order to achieve the depth that the technology offers. Passive and Active 3D achieve this using different methods, both of which have their advantages and pitfalls. And while there’s no clear winner, we thought we’d come up with a little article to help decide which 3D is right for you.

Passive 3D

Passive 3D is perhaps the method people are most familiar with. Because of the relatively inexpensive polarised glass that’s used, it’s what’s used in most multiplex cinemas, although now it is also starting to be used for televisions.

Passive 3D televisions use a built-in polarising filter to evenly divide the number of pixels that each eye sees. Whilst the image appears normal without glasses, with glasses the left eye will only see odd lines of pixels and the right eye will see even lines. Each eye, therefore, only sees half of the image, or 1920 x 540 pixels. This leads to interlacing and jagged diagonal lines, whose visibility depends on the size of your screen and the distance at which you sit from it. Typically, the glass used lets through more light. The glasses themselves weigh and cost less, and are generally more comfortable to wear.

Active 3D

Active 3D is predominantly an invention for 3D LCD, LED, plasma screens and home projectors. The glasses use battery-operated shutters in both eye-pieces to rapidly open and close alternately, resulting in image information intended for your left eye being blocked from your right and vice versa. Your TV needs to be able to refresh at a speed where each eye gets at lest 60 frames per second in order for this to work effectively.

The main advantage here is that with Active 3D, each eye is getting a full 1080p image, rather than having it split across both eyes. However, the glasses tend to be heavier and more expensive. They also let less light in, making the image appear dimmer, especially on projectors due to their typically lower brightness/contrast ratios. Depending on your eyes, it’s also possible to be aware of the rapid shutters at work, either visibly — such as an intrusive flickering effect on the image — or in a more uncomfortable, subconscious way, which could hamper your viewing experience.

 

In summary: Passive 3D is a more comfortable and perhaps more cost-effective solution, but offers what could be viewed as a compromised image. Active 3D arguably offers better image quality, but the glasses required are more expensive and potentially yield a more uncomfortable viewing experience depending on personal eye sensitivity. Ultimately, the decision depends on the amount of 3D content you plan on watching.

 

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