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There is a lot of 3D movies out there in these days, but they are also released in 2D (dvd, blu-ray, ...). I think, they are originally captured as 3D movies (with stereo camera). So each frame has 2 versions - one for left and one for right eye.

How are they transferred to 2D?

I have some candidates:

  • Only one (better looking) version of frame is taken
  • Only one version (the same version for whole movie, i.e. only left) of frame is taken
  • They are somehow combined together, because we don't want to lose any information (how are they combined?)
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    Since both eyes don't differ that much, I guess they just take one eye's version for the whole movie, but well, I don't know it.
    – Napoleon Wilson
    Commented Jan 23, 2012 at 12:47

2 Answers 2

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The question begins with an incorrect assumption. Currently, when movies are made, they are mainly made for 2D setups (i.e. theaters, and home systems). Due to the different ways films are made, this has to be broken out into different options:

  • For live action films where they are recorded in 3D, they can just use one of the two images they've filmed for the 2D version. There shouldn't be a 'bad version' as the question supposes, because if there is a marked difference in quality between the two, then that will negatively impact the 3D presentation of the film.
  • For live action films not recorded in 3D, they have to alter the 2D footage to create the 3D footage. This is called post-production conversion.
  • For CG animated films, they'll create both in concert, and will sometimes create subtle differences created in the 3D version. (see Tangled for example)
  • I don't know of any non-CG animated films that have been released in 3D, so I guess this is one is unknown.

Comparison shots of Tangled's 3D and 2D versions follow. You can see the differences in the backgrounds, look at the trees and see how they're in clear and in focus in the 3D version, but blurry in the 2D version. Similarly the fields in the background are clear in 3D, but blurry in 2D. 3D version 2D version

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From the Disney Blu-ray 3D help site:

When you're watching a 3D/2D compatible disc in 2D, you are actually watching a single eye view of your film (i.e. the left eye or right eye only).

I would imagine this is the method used in theaters as modern 3D films are digital projections and thus can be altered accordingly - so Christian was on the right track.

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    Good reference, but is that the entire story? That is how you get a 2D playback from a blu-ray disk containing a 3D compatible stream. This saves a lot of storage space compared to storing a 2D and a 3D stream on the same disk. Is the 'one half of a 3D movie' exactly what they release as a 2D only dvd/blue ray or in the theatre. @Keen's answer suggests otherwise (in some cases anyway).
    – iandotkelly ♦
    Commented Jan 24, 2012 at 5:36

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