What is the difference between active and passive 3D

Modern 3D TVs offer two technologies for «three-dimensional visualization» of content — active and passive. And there is a rather serious difference between them, which manifests itself not only in price, but also in the quality of the display.

But to understand the difference between active and passive 3D, you need to know how «3D rendering» works in principle.

How 3D technology works

There is only one way to get a three-dimensional (3D) image from a flat screen — by transmitting a separate image to the left and right eyes. Then the brain will be «deceived» and independently complete the visual, making it three-dimensional.

However, how to submit a separate picture to the left and right eyes, if there is only one television screen? This is achieved due to a small «duplication» of the video stream. When viewed with a naked eye 3D effect, the video appears too blurry.

In fact, the video is not blurry, it just consists of two video streams — one for the left eye, the second for the right. And special glasses allow you to separate them.

These accessories are of three types:

1. 
   Passive anaglyph. This is one of the first 3D glasses. In them, one glass is painted blue, and the second is red. Because of this, each eye sees a different part of the image (either with a blue or red shift);

2. 
   Passive polarized. Similar glasses are used in cinemas for films with 3D support. However, they are also suitable for home use. The glasses or films in them have different polarizations, which is why each eye sees its own half of the “picture”;

3. 
   Active shutters. The most advanced rendering technology for 3D video. Each glass of glasses in it is a small LCD display that either closes or opens access to the video to the eye.

Each of these technologies has its own advantages and disadvantages.

How Anaglyph Passive 3D Works

Anaglyph technology is one of the first 3D rendering mechanics. To watch movies with its support, you will need special blue-red glasses.

When viewing anaglyph 3D video with the naked eye, the image appears to be doubled. Blue and red plumes appear behind each object. But it is worth putting on this necessary accessory — and the “picture” from the screen will be transformed into three-dimensional.

The fact is that the blue light filter does not let the blue loop through, and the red one does not let through the red one. Because of this, each eye gets its own picture, in which the positions of objects differ. That is why there is a 3D effect.

Anaglyph passive 3D was most common in the 80s of the last century. However, due to the huge number of shortcomings, it was soon forgotten. And it was replaced by the mechanics of passive 3D with polarization.

Should you buy an anaglyph passive 3D TV in 2019?

Anaglyph passive 3D does not require any special screen characteristics. So this video can be played on absolutely any TV screen. Even if your TV does not support 3D, you can still buy blue and red glasses and watch a «three-dimensional» movie.

How passive 3D with polarization works

Passive 3D uses polarization technology. In fact, thin horizontal, vertical and circular stripes are applied to the lenses of the glasses, which do not miss part of the image. Thanks to this, each eye receives its own “picture”, and the brain already “finishes” it to a full-fledged 3D.

There are several polarization options for passive 3D. The simplest and cheapest one is that stripes are applied horizontally on one glass, and vertically on the second. Because of this, each eye receives its own half of the picture.

The main disadvantage of this 3D rendering method is the degradation of 3D quality when the head is tilted. Watching such films or videos is only right in front of the TV and without leaning on it. In addition, polarization «eats» the detail due to the deterioration in resolution.

Let’s say you’re watching passive 3D on a Full HD resolution matrix — 1920×1080 pixels. Then, after horizontal polarization, an image of 1920 × 540 pixels is presented to the eye; and after vertical — 960×1080 pixels. Because of this, the detail is reduced.

The brightness is also reduced. And this is also due to polarization.

Both of these shortcomings are devoid of glasses with circular polarization. With them, you can safely tilt your head, watch movies lying down and in other positions. Also, the loss in detail is slightly less, although only half of the image is still fed to each eye.

Should you buy a passive 3D TV in 2019?

If the budget is limited, and you want 3D, you can buy such a TV. But it is better to pay attention to models with circular, rather than horizontal-vertical polarization.

How active 3D works

Active 3D is the most advanced 3D imaging technology. It implies that the video must be watched with special shutter glasses. The glasses in them are equipped with small LCD displays that become transparent or opaque depending on the TV command.

While one glass is transparent, the other is opaque. Then they change. The frequency of switching modes is up to 30 Hz (once per second) depending on the specific TV model and movie frame rate.

As a result, while watching such a film, one eye is open, the other is closed, and this state is constantly changing. And the brain «finishes» itself.

Active 3D requires both the TV and the glasses to support it. The latter, by the way, run on batteries and communicate with the TV via infrared.

Should you buy an active 3D TV in 2019?

Yes, definitely worth it if you want to frequently watch 3D videos with family or friends. But you should be prepared for the fact that you will have to pay a kilogram of money for additional points for the rest of the audience.

Which is better — active or passive 3D?

When it comes to the quality and detail of graphics, the ability to calmly walk around the room or lie on the couch while watching a movie, then, of course, a TV with active 3D is better. But you will have to pay for this. And literally, active 3D glasses are quite expensive; and figuratively — the eyes get very tired, a headache appears.

If you want to save money, and you plan to watch movies every couple of weeks at best, then passive 3D will suffice. Unfortunately, this technology reduces detail, but for the sake of the «wow effect» you can sacrifice the visibility of each element against the background.