What does 3D actually show us?

[AlmaataKZ]

In other words, how exactly does it work?


Say, we have a modern HD screen – the best resolution image it can show is 1920 vertical by 1080 horisontal pixels or lines. It can show, say, 24 frames per second in this resolution, some sets (100Hz, 200Hz refresh rate) can show more, although when they show more they show the same frame several times (4 or 8), or sometimes interpolate frames. Correct?


Now, let’s take two of today’s main sources of video signal: TV (cable, sat or terrestrial) and BluRay disc.


The maximum TV has reached today in terms of resolution broadcasted is 1080i (interlaced), i.e. every second it shows one of the 12 half frames on 540 horisontal lines, then one of the 12 half frames on the other 540 horisontal lines and so on until all 24 frames are shown. This means your eye, every 1/24 of a second, sees only half of the frame and then your brain has to ‘blend’ them with the next half frame (every 1/12th of a second) and then ‘blend’ these half frames into one whole second of movement. Correct?


The maximum BluRay has reached today in terms of resolution is 1080p, i.e. every second it shows full 1080 horisontal lines 24 times per second. This means your eye, every 1/24 of a second, sees a full frame and then has to ‘blend’ them into one whole second of movement. Correct?


Now, what do we do to get 3D effect? Each eye has to see a different picture for your brain to interpret the picture as 3D.
Let’s take one complete second of a movie again, in case of BluRay, split into 24 frames of 1920 x 1080 lines.
3D ‘active’ version means that the TV shows an image for one eye half of the time and for the other eye the other half of the time. So, it will show a full frame for 1/24 of a second for the left eye (while the left part of the glasses is open), then a full frame for the right eye (while the right part of the glasses is open). These two frames probably have been recorded (filmed) at the same time (but then shown one after the other) or shot one after the other and shown one after the other. Regardless, the amount of video information each eye sees over each full second has halved. Correct?


3D ‘passive’ or polarised version means that the glasses do not open and close but one eye remains permanently blacked out for the light polarized at one plane and the other eye is permanently blacked out for the light polarized in the other plane (angled at 90 degrees). So, the TV can show, at he same time, an image mix for both eyes (if pixels are polarized differently) and the glasses ‘pass through’ the relevant part of the image for each eye. So, the TV will show a full frame for 1/24 of a second but half of this frame is for the left eye and half is for the right eye. These two superimposed half frames have probably been recorded at the same time and are shown at the same time. Again, the amount of video information each eye sees over each full second has halved. Correct?


That was Bluray. What about TV – 1080i?


For 1080i we already had to half the number of lines. If we now want to get 3D effect, we need to split the frames between the eyes, again halving the number of frames (loosing on smotheness fo movement) or frame size (loosing on resolution). I.e. seeing only quarter of the video information if compared to non-3d full HD.


Is that correct?


So, does 3D mean a drop in picture quality (to half on Bluray and to one quarter on TV)?


I understand it may not be that simple (there may be interpolation, lossy or lossless compression etc involved), but as the bandwidth capacity of the format is limited to max 1080p or 1080i, the only way to squeeze 3D effect in is by loosing quality.
Once again, a step forward, a step back?

 

[Clare Newsome]

Not quite right - active-shutter 3D systems can deliver a full HD frame to each eye in turn, so there's no loss in resoluton.

There's far more on this - including discussion of deinterlacing - in our 3D TV Jargon Buster feature; page 80 of the current, October issue.

 

[Anonymous]

there's definitely a loss in the vibrance of colour with the 3D glasses, I'd be interesting for someone to do a side by side 2D/3D test of the same movie to look at the resolution differences.

I heard 3D is basically a scam for multiplex cinema companies to make more money; an extra £2/person charge will mount up, allowing them to buy new screens eventually. I don't know how true this is, but I'm pretty happy with the quality of Blu-ray.

 

[FunkyMonkey]

My understanding is that with 3D you get the same number of frames PER EYE as 2D, so in effect you get double the frame rate overall.

So yes the film is recorded at 24frames per second, but as you say two pictures in each frame, one for each eye.

BUT that is played back at 48 frames per second, or multiple thereof, with active shutter glasses systems. So odd frames are for left eye and even frames for right eye, for example.

 

[AlmaataKZ]

Clare Newsome:

Not quite right - active-shutter 3D systems can deliver a full HD frame to each eye in turn, so there's no loss in resoluton.

There's far more on this - including discussion of deinterlacing - in our 3D TV Jargon Buster feature; page 80 of the current, October issue.

thanks, will have a look.

 

[Andrew Everard]

jsl20:I heard 3D is basically a scam for multiplex cinema companies to make more money; an extra £2/person charge will mount up, allowing them to buy new screens eventually.

You heard wrong: showing 3D in cinemas requires a substantial investment in projection equipment, glasses, and a new screen: that's why relatively few cinemas are kitted out for 3D, and companies like Technicolor are working on ways of enabling more screens to handle 3D content at lower cost.

 

[AlmaataKZ]

Clare Newsome:

Not quite right - active-shutter 3D systems can deliver a full HD frame to each eye in turn, so there's no loss in resoluton.

FunkyMonkey:

My understanding is that with 3D you get the same number of frames PER EYE as 2D, so in effect you get double the frame rate overall.

So yes the film is recorded at 24frames per second, but as you say two pictures in each frame, one for each eye.

BUT that is played back at 48 frames per second, or multiple thereof, with active shutter glasses systems. So odd frames are for left eye and even frames for right eye, for example.

Ability of the 'format' to deliver is good.

Does this mean the media (bluray, TV) and hardware (TVs, BDPs) need to step up thespec to utilise teh 'full-rez' potential of 3D?

And how big the share/penetration of the 'full-rez' 3D will be to the consumers? I mean, how good teh 3d at home can be in 2010?

 

[AlmaataKZ]

jsl20:

I heard 3D is basically a scam for multiplex cinema companies to make more money; an extra £2/person charge will mount up, allowing them to buy new screens eventually. I don't know how true this is, but I'm pretty happy with the quality of Blu-ray.

I doubt it is a scam. it is business, and technical compromises are to be made.

Just trying to understand what they are and how much of a 'step back' if any is accompanying the 'step forward'/

 

[FunkyMonkey]

AlmaataKZ:

Ability of the 'format' to deliver is good.

Does this mean the media (bluray, TV) and hardware (TVs, BDPs) need to step up thespec to utilise teh 'full-rez' potential of 3D?

And how big the share/penetration of the 'full-rez' 3D will be to the consumers? I mean, how good teh 3d at home can be in 2010?

The only thing 3D Blu Ray players as opposed to 2D blu ray players have to do is be able to put out double the number of frames per second. I can't see any other advancement.

I watched 3D on Panasonic plasma with shutter glasses last year and the resolution was as good as Blu Ray 2D in every way but 3D. No colour or resolution degradation liek you might get with polarised, i.e. at cinema.

In other words, teh technology is good to go...if you don't mind wearing glasses.

 

[Anonymous]

AlmaataKZ:jsl20:
I heard 3D is basically a scam for multiplex cinema companies to make more money; an extra £2/person charge will mount up, allowing them to buy new screens eventually. I don't know how true this is, but I'm pretty happy with the quality of Blu-ray.

I doubt it is a scam. it is business, and technical compromises are to be made.

Just trying to understand what they are and how much of a 'step back' if any is accompanying the 'step forward'/

alright, maybe "scam" isn't the most appropriate word to use; its a clever business strategy. i went into my local hi fi store to get a quick 3D demo this afternoon, but someone had played with the TV's settings and it wouldn't play the movie, so i still can't really compare 2D to 3D full HD.

 

[Anonymous]

Ive been to see 4 3D movies lately and i only had to buy the glasses once just remember to bring them with you when going to see a 3D film. £2.00 isnt much of an outlay and hardly a "rip off"

 

[strapped for cash]

It's hardly a scam (i.e you get what is advertised, whether you like it or not).

Entertainment conglomerates have perhaps made a mistake investing in a product that isn't in line with consumer demand. Then again, various industry officials and filmmakers (Alfred Hitchcock included) said the introduction of sound "signalled the death of pure cinema."