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 — 1920x1080 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.