[Tig] 3D systems
richard at filmlight.ltd.uk
Wed Jan 6 09:26:44 GMT 2010
How different are the various systems?
As I understand things, there are four options...
(1) Conventional polarization
Cheap glasses, second image if you head is not straight, needs silver
(2) Rotational polarization
Phase difference between two polarizations. Little second image for
normal head tilts. Still needs silver screen. Glasses more expensive.
(3) Colour multiplexing
Dolby 3D (Inifitec). Different wavelength RGBs for either eye. Does
not need silver screen. Glasses currently expensive. May need special
(4) Shutter glasses
Expensive active glasses. Does not need silver screen.
There seem to be two major differences...
The silver screen options will generally have less luminance
uniformity. It should be possible to make a smarter screen that keeps
polarization using something like tiny cube corner reflectors, but
these are not generally available, and cinemas won't have them.
All of these systems can be used to serve alternate images to either
eye. When driven like that, they will give a frame flicker that will
become tiring for peripheral vision except for very high frame rates.
Options 1-3 can use two projectors in parallel, which allows you to
double the light level. Low light level is often a problem with 3D, so
adding a second projector is not a silly thing to do for a cinema.
On this reasoning, the colour multiplexing (Infitec) solution would
seem to be best when using two projectors. However, the Infitec
filters mean that only about 14% of the projector light gets to the
eye, whereas the polarizer solutions manage almost 25% (half goes at
the projector, half at the glasses). If shutter glasses went 100%
clear, then they would manage 50% overall efficiency, but currently
they use LCDs and so are stuck at 25%.
If you can get enough light, then the calibration solution would seem
to be to calibrate to deliver the same 16 ft-L D60 white to either eye
when wearing 3D glasses. If you go much dimmer than this, then color
vision gets non-linear, and the colors can look wrong. I think we
ought to increase the light level in cinemas anyway: if we don't then
cinemas are going to start looking dimmer than home computer displays
and projectors in small rooms.
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