Originally Posted by NeilF
So a 1 second piece of film will have say 24 frames on the 2D version, but 48 frames for the 3D version?
I think I know where this is coming from.
You want to know whether a 3D BD has lesser video quality because you think a fixed size limit on the BD disc [currently 50GB] means the studio had to lower the video quality to accomodate twice
the data you are assuming is needed for 3D [L & R eye].
First, to answer your question, the answer is no, the 3D version is till 24fps [technically 23.976 fps but thats another thread
Remember, 3D is frame-packed so in the timespan where only one 1920x1080 frame would be sent out in 2D [approximately 24th of a second], one large frame is sent out in 3D.
This large frame is two 1920x1080 frames sitting one on top
of the other with a 45-pixel height black image in the middle resulting in one 3D frame having a dimension of 1920x2205 [1920x2160 + 45]
Now, although the large 3D frame is still sent out at 24fps, the question of storage still comes into play.
The BD spec engineers realised that if they stored the extra second frame for 3D with the same compression they use for the one 2D frame, they would not have enough space on the disc so they decided to store the information for the other eye as difference
data, meaning only the differences between the frames are stored and used to generate
the information for the other eye which is done by the player.
This allowed for much less storage space being needed and, thus, the quality of the 3D video is the same as the 2D version.
Keep in mind that the brain will perceive higher quality on 3D releases because each eye gets its own separate 1080p image but this is not what you were asking out, at least not to me.