Why Does Ghosting Occur in Polarized 3D Movies?

[junglebeast]

I watched Avatar in Real3D and IMAX 3D. This is the first 3D movie I have seen at the theater. However, it was also clear that this 3D technology has a fair bit of room for improvement.

Specifically what I noticed was that the perceived images have a bit of ghosting in them. This is most easily noticed in the beginning before the actual movie starts when they just show some writing against a solid background, and you can see a ghosted version of the letters floating to the side of the actual letters.

I also noticed my brain having a difficult time correlating some of the extreme depth changes -- something that my vision system is perfectly capable of doing in the real world, and does not cause me an active feeling of strain and headache as it did in the theater.

Because of the way the film was rendered and stereoscopically recorded, I know that the left/right images have to be perfect, meaning that these problems are introduced by the method of displaying the movie rather than the actual movie itself.

My hypothesis is that when the polarized image hits the projector screen, there is some amount of diffusion which slightly changes the polarization. This could cause the glasses to allow a small percentage of the right eye view to leak into the left eye, and vice-versa...which would explain why I saw ghosting, and why it was difficult to correlate.

If my hypothesis is correct, then the viewing experience should be significantly more realistic when viewed using the active shutter technology instead...but I don't have a 3D TV to test it out. Does anyone have a 3D TV or LCD that can confirm ghosting does not appear there as it does in the movie theaters?

 

[Edgardo]

My hypothesis is that when the polarized image hits the projector screen, there is some amount of diffusion which slightly changes the polarization. This could cause the glasses to allow a small percentage of the right eye view to leak into the left eye, and vice-versa...which would explain why I saw ghosting, and why it was difficult to correlate.

This seems to be right. There is a nice blog post by Lenny Lipton on http://lennylipton.wordpress.com/2010/01/13/polarized-light-and-3-d-movies-part-1/" he writes:

That is because the polarization-conserving metallic painted screens are imperfect; and since they are imperfect, the total dynamic range of the system is reduced. [...] Still, with a dynamic range of 200:1 you can have a good picture with low cross talk between the left and right images. Such cross talk is called ghosting in the argot of 3D; or sometimes leakage.

In http://lennylipton.wordpress.com/2010/01/18/polarized-light-and-3-d-movies-part-3/" he writes:

When you look at a stereoscopic image through a selection device, whether it’s linear or circular, there is a certain amount of light that leaks through (as noted earlier it’s called leakage) because of the incomplete extinction of polarization. This leakage results in what is called a “ghost image.” So there is some crosstalk between the left and right images, and you may see a bit of the left image through the right eye and vice versa. It can look like a double exposure.

Besides, more on Lenny Lipton:
http://en.wikipedia.org/wiki/Lenny_Lipton
http://www.lennylipton.com/

Lenny Lipton was involved in the development of stereographic projectors.

 

[junglebeast]

Great, thanks a lot for finding this