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Author Topic: How do 3D movies or films work?  (Read 12321 times)

Quinton Greyling

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How do 3D movies or films work?
« on: 20/07/2009 19:30:03 »
Quinton Greyling  asked the Naked Scientists:
   
Thanks for your programme - I follow this on podcast from South Africa.

This past weekend I went to watch Ice Age in 3D. I would like to know how they create the 3D effect? Looking at the screen without the glasses it looks blurry; with the glasses, the effect is quite good. How does the glasses work?

Also, how did the older version (the red and blue) glasses work and how is this different to the current technology.

Thanks,
Quinton

What do you think?
« Last Edit: 21/08/2009 18:48:56 by chris »


 

Offline LeeE

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Re: How do 3D movies or films work?
« Reply #1 on: 20/07/2009 20:49:19 »
There are a few different ways to produce 3D effects on screens but I suspect the technique you saw used 'interleaving'.

This technique was developed from the old method of 'painting' pictures on early black and white crt raster displays where lines are drawn across and progressively down the screen, the brightness of the line varying to produce the light and dark areas.  If you can do this quickly enough, so that the whole screen can be painted in less than about 1/25th of a second, our eyes only perceive the overall image and can't see the drawing process (incidentally, flies can see more 'quickly' than us i.e. they can optically resolve shorter periods and can see this drawing process occurring, which is why they seem to have such fast reactions when we're trying to swat them).

Anyway, due largely to broadcast bandwidth constraints, it wasn't possible to transmit a full screen's worth of data quickly enough i.e at 25 frames per second (fps).  To get around this and stay within the bandwidth limits, instead of trying to broadcast the full set of lines for each image, one after the other, alternate lines were broadcast for each frame i.e all the even numbered lines, then all the odd numbered lines and this, together with the long persistence phosphors that were being used in the crts looked, to the human eye, like complete frames.

Modifying this to produce 3D is relatively straightforward.  Instead of displaying alternate temporal lines, you display alternate spatial lines, each lens in the glasses actually being a shutter that's syncronised to the display interleaving so that the left eye only sees the lines that correspond to the left spatial image and the right eye only sees the right spatial image lines.  Do it quickly enough, and at a high enough resolution, which isn't too much of a problem in a cinema where there're no bandwidth constraints, and you'll appear to see a single smooth image.

Another variation on this, where the image isn't rasterised, is to display entire alternate images, once again using the shutter glasses to ensure that each eye only sees its corresponding image.

The old red/blue glasses worked by filtering the left and right spatial components from a single image where both were overlayed at the same time.  This required the two spatial images to be tinted though, of course.
 

Offline chris

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Re: How do 3D movies or films work?
« Reply #2 on: 20/07/2009 23:21:44 »
CAn you not polarise the images and then use polarising filters on the glasses, which will effectively screen out one image for each eye; when the two are superimposed on the brain you see 3D.

Chris
 

Offline JP

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Re: How do 3D movies or films work?
« Reply #3 on: 21/07/2009 00:15:03 »
CAn you not polarise the images and then use polarising filters on the glasses, which will effectively screen out one image for each eye; when the two are superimposed on the brain you see 3D.

That's how most modern films do it, I believe.  Modern films use circular polarization, so that tilting your head won't destroy the effect.

Most modern 3D films are "RealD," and you can read a bit about it on Wikipedia:
http://en.wikipedia.org/wiki/Real_D_3D
 

Offline LeeE

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Re: How do 3D movies or films work?
« Reply #4 on: 21/07/2009 18:27:57 »
Hmm... Ice Age is included in the list of RealD films so it probably was RealD that the questioner saw.  I didn't mention polarising techniques because I wouldn't have described them as looking 'blurred' without the glasses; they look more like double-vision to me, whereas interleaving does make the edges of things seem blurry.
 

lyner

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Re: How do 3D movies or films work?
« Reply #5 on: 21/07/2009 22:30:06 »
Film has a great advantage over TV because you can use two different sources of image. The circular polarisation from two projectors is a brilliant solution - requiring nothing but a pair of cheapo glasses to see it. For TV, they need to be able to make an LCD screen with minuscule circular polarisers for each pixel plus an different way of addressing the pixels in order to put alternate left eye / right eye signals on adjacent pixcels. Any other method of switching between left and right images involves special glasses, linked to the display, to allow the appropriate picture to reach each eye.

But you can never discount the possibilities in future technology.

There is one proviso, though. There are only a limited number of satisfactory viewing positions for good stereo viewing with this crude basic two - image system.

I think it will never be more than a novelty until there is something radically different for 3D viewing. Stereo is  only of any use in portraying relatively close up images or exaggerating spacial arrangements.
 

Offline JP

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Re: How do 3D movies or films work?
« Reply #6 on: 22/07/2009 03:37:21 »
The recent RealD stuff gets away with one projector and a circular polarizing filter in front of it, so you can get away with one projector and a pair of (passive) polarized glasses.  Some of planned (and maybe by now current?) 3D televisions use passive glasses as well, but have alternating polarization lines on the display to achieve the same effect.
 

lyner

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Re: How do 3D movies or films work?
« Reply #7 on: 22/07/2009 09:18:43 »
That must demand very good registration of the image on the filter so the stripes of left and right image hit the appropriate polarisation. Likewise for a TV display (but not a problem for a non raster display).
But mis registration will only produce a bit of fuzziness; not too disturbing.
 

Offline gurpal

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Re: How do 3D movies or films work?
« Reply #8 on: 22/07/2009 16:26:02 »
i really dont under stand why and how thw fussy image becomes 3-D and clear with the glasses
 

Offline JP

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Re: How do 3D movies or films work?
« Reply #9 on: 22/07/2009 18:39:14 »
i really dont under stand why and how thw fussy image becomes 3-D and clear with the glasses

You see real life objects in 3D because each eye receives an image of the object from a slightly different angle, and your brain knows how to put these two images together to make it look 3D.  The fuzzy image in a 3D movie is actually two different images mashed together.  The glasses work by only allowing one of those two images into each eye, so that each eye receives a slightly different image, and (just like in everyday life) your brain combines those images to make it look 3D to you.  All 3D movie/television techniques come down to making sure each eye gets a slightly different image.
 

lyner

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Re: How do 3D movies or films work?
« Reply #10 on: 22/07/2009 18:45:18 »
This is done ever so simply, in stereoscopy and there is only one viewing place where it is 'correct'.
For true 3D vision, you need to make the image look right for a whole range of viewing angles. This is why the Hologram is so clever. The problem would be the vast amount of information which would be needed (and the processing, too) to  produce moving holograms a la Star Wars Princess sequence but which would look at least as good as our 2D telly pictures.
 

Offline RD

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Re: How do 3D movies or films work?
« Reply #11 on: 05/12/2009 14:20:52 »
... The problem would be the vast amount of information which would be needed (and the processing, too) to  produce moving holograms a la Star Wars Princess sequence

See ...
, the jogger @ 4:25 is very princess Leia.

It's a bit like a 3D version of the Baird Televisor (mechanical television).

« Last Edit: 08/12/2009 02:10:54 by RD »
 

Offline who is this?

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How do 3D movies or films work?
« Reply #12 on: 08/12/2009 00:59:19 »
i dont watch 3D films, i have no depth perception lol
 

Offline Tommyboy

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How do 3D movies or films work?
« Reply #13 on: 12/12/2009 09:14:28 »
Any watch Avatar in 3d?
 

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How do 3D movies or films work?
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