difference between active and passive 3d glasses

What is the difference between active and passive 3D glasses?

It would seem that 3D television technology has fallen out of favor with the general population in recent years. However, this is farther from the truth since there's still a dedicated fan base of 3D movie lovers. Thanks to the engineers from major companies that produce TVs, like Panasonic, or LG that is also about to change.

Additionally, the number of educational facilities and government agencies turning to 3D imaging continues to grow by the day. The benefits of 3D projectors, monitors, and displays are becoming increasingly acknowledged in education and training. But to make it all work, you need 3D glasses. And not just any 3D glasses; the ones you choose must correspond to your display type.

Today's article discusses the difference between active and passive 3D glasses and their respective technologies. In it, we'll also discuss some of the basics of 3D image technology, how stuff works, and individual advantages and drawbacks. To begin with, let's see how 3D technology works.

How does 3D technology work?

To understand the difference between active and passive 3D glasses, first, we'll have to know how 3D technology works.

As we all know, the image displays are mostly flat 2D surfaces, like monitors, screens, and image projector backgrounds. So, it stands to reason that flat 2D surfaces create flat 2D images, and for those images to appear as 3D, some illusions are put to work.

3d glasses

There are two types of 3D technology you can choose from today, active 3D or passive 3D. Of course, both technologies work differently, with their own advantages and drawbacks, but they all exploit our brain's image post-processing capabilities.

When immersed in a viewing experience, such as watching a movie, our brains do a ton of auditory and visual post-processing. Your brain does a lot of work to interpret the visual input from your eyes, including height, width, and most importantly, depth. 2D image, like the one on your screen, has only height and width. But what about the depth?

Well, if you slightly offset the visual inputs independently sent to your left and right eye, the brain will start perceiving depth on a 2D image. In other words, you're tricking the brain into overlaying 2D images from each eye respectively to create a 3D image. Keep in mind that we only explained the basic principle, and modern 3D technologies employ other, far more complex methods to create a 3D image.

The devices that display and help you view 3D images do so by offsetting the images sent to your eyes. If you were to close one eye, you wouldn't see a 3D image, and you will continue to perceive it as a flat 2D projection.

The technology used to achieve such effects is either active or passive and refers to the glasses and the display.

The difference between 3D glasses technology

To be able to see a 3D image from your display (a TV, monitor, or projector), you'll need a set of 3D glasses. And you'll need ones that correspond to the type of 3D technology your viewing display uses, e.g., active 3D glasses for an active 3D display.

All 3D images work on the same principle: the brain constructs a three-dimensional picture by post-processing slightly offset visual inputs. So, what is the difference between active and passive 3D?

Well, the difference lies in how these effects are achieved.

Active 3D glasses technology

Active 3D glasses require a power supply to operate LCD shutter lenses, which rapidly shutter open and close. These are usually battery-operated but can be powered via a UBS cord if you're using them on your laptop or computer.

Active 3D displays show sequential frames of 3D footage to each eye, sequentially displaying frames for your left and right eye. But the glasses electronically block or shutter the lenses, in sync with the 3D display. That way, they block your left eye from seeing the frames meant for your right eye and vice versa.

The frames of 3D footage shown to the left eye are horizontally shifted from those shown to the right eye. And since they alternate at 60 frames per second for each eye, the screen's image will appear 3D.

Note: If you wants to know which Active 3D glasses is best suited for you then you should read this article from our blog

Passive 3D glasses technology

Most people experienced passive 3D when watching a 3D movie at a movie theater. Some might even remember those old ones with red and blue lenses that appeared around the 1950s. Well, modern passive 3D works on the same principle but with full-color images.

passice 3d glasses

Passive displays blend two frames in one, alternating between horizontal lines meant for one eye and the one meant for the other. They use specialized filters that work with the polarized lenses in your glasses.

The polarized lenses block out either the even or the odd lines on your display. That way, your left eye can only perceive odd lines, and your right eye sees only even ones. The overlay created by our brain's visual post-processing creates the 3D effect. Interestingly, without the glasses, the display's image looks entirely 2D and has no crosswalk as active 3D does.

What kind of 3D technology is better?

Unfortunately, there's no straight answer to this question since both have their uses and drawbacks. Active 3D displays better images but features a hefty price tag. Passive 3D, on the other hand, is more broadly used due to its low-price and simplicity.

In most cases, where active 3D excels, the passive 3D falters, and the same can be said the other way around. Here are some decisive factors:

Resolution

Active 3D uses advanced electronics, circuitry, and battery power, so it takes the win when it comes to image resolution.

Active 3D uses alternating frames sequentially shown for each eye at a full native resolution of the footage. Passive 3D splits the frame's vertical resolution between the left and right eye; therefore, the vertical resolution is halved.

Though it sounds like a significant difference in theory things are a bit different. The resolutions between the left and right frames of passive 3D are indeed halved. But our brains are fantastic at visual post-processing and blend the picture back together.

The difference between the two is just slightly perceptible at 1080p resolutions and almost entirely invisible with 4K. 4K resolutions have twice the number of vertical lines, making the reduction even less noticeable.

Still, the winning position goes to Active 3D because it does not alter the image resolution in any way.

Image Quality

Passive 3D suffers less image crosswalk and less motion lag, taking the win in the aspect of image quality.

Crosswalk, or ghosting, happens when the glasses aren't in perfect sync with the active 3D display. When that happens, the information meant for one eye is picked up by the other, creating an effect of two superposed images. This can happen for many reasons, like the TV's response time issues or faulty glasses.

Passive 3D glasses display crosswalks at a significantly lower rate than active 3D, to the point where it's almost invisible. The same thing happens with motion. Active 3D shows left/right frames sequentially, and sometimes, information gets picked up by the wrong eye or doesn't get picked up at all.

Our brains might perceive this as a difference in depth instead of motion, diminishing the quality of the 3D effect. It can even introduce fatigue as the brain struggles to compensate for the missing movement or increased depth.

The only aspect in which both technologies are at a draw is the image brightness. With active 3D, one of the lenses is black at all times, while with passive 3D, every second line is black. This brings the overall brightness down, but most TVs nowadays increase the brightness to compensate.

Comfort

Passive 3D glasses don't have any advanced circuitry and batteries like active 3D glasses; hence, they're usually lighter and more comfortable. But weight isn't the biggest problem – flickering is. 

Active 3D models will, due to alternating shutters, cause a flickering effect on otherwise flicker-free TVs. This can cause discomfort and headache when watching 3D footage, and it's impossible to avoid, regardless of how advanced your active 3D is. 

Price

Passive 3D glasses lack electronic components and connectivity, with a more straightforward manufacturing process behind them. This makes them more accessible in terms of price but imposes all the passive 3D technology limitations, like reduced image resolution.

So, if you're on a budget, passive 3D glasses are excellent since they're affordable and compatible with most systems. However, if you're looking for an ultimate viewing experience on your TV or a projector, active 3D, albeit pricier, displays more details.

Conclusion

As a more technologically advanced product, active 3D glasses take over the market, despite the higher price tag. They have better overall image quality and more ease-of-life features, like Bluetooth, when compared to passive 3D.

Ultimately, it would be best if you got glasses that are compatible with your current 3D system. If you're looking to invest in the ultimate viewing experience, we would suggest an active 3D system with compatible glasses. But if you're looking for broader compatibility and lower price, passive 3D is the way to go.

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