[robespierre]

The CrystalEyes glasses are always open on either the right or left side. They switch directly from left to right without any dead time. So no time at all (0 ms) is available for refreshing a screen from one view to the other. This works with a CRT because the phosphor persistence is short. By the time the beam finishes drawing the bottom line, the top half of the screen is black. By the end of the vertical retrace, the whole screen is black. If the glasses are timed to switch at that moment, the eye on the new side will not see any light from the previous eye's view (there is a tiny amount of afterglow from the phosphors, about 1%).

The other important fact about all VESA stereo glasses is that they are synchronized with the video output of the computer system. A CRT has zero latency from when the image data leaves the RAMDAC in the graphics device to when it appears to the eye. By putting the glasses under control of the computer, the switchover time is coincident with the vertical retrace interrupt and the flipping of the active display buffer. LCD displays work differently because they are digital and receive data in packets (over DisplayPort or HDMI). Image data is queued up and processed in chunks, leading to latency from the computer's graphics output. LCD monitors with 3D ability generate and transmit the synchronizing signal from the monitor so it remains locked to what the eye sees.

All of the above is perhaps solvable with enough thinking and work. The stereo timing signal could be adjusted or delayed based on the LCD panel latency. The left and right frames could be interspersed with black video frames to ensure that each eye starts out viewing a black screen. Some fancy-dancy FPGA box could digitize the signal and insert these changes (like the GBS converter does for CGA signals). But a problem is lurking within these anodyne descriptions. LCD displays work by polarizing light. There is a polaroid film behind and in front of the liquid crystal panel. The liquid crystals can be twisted or untwisted to control the angle of polarization, to allow the light to pass or be blocked. Then you see the light that had the proper polarization to pass the front polaroid film. LCD shutter glasses work by polarizing light... See the problem? If the light from the screen is polarized against the front polaroid film of the glasses, they will be forever dark, whether the shutters are on or off. Luckily most LCD screens seem to be vertically polarized, while CrystalEyes are at 45 degrees, so some light does get through. It looks dim and washed out, not nice at all. For a similar reason, 3D movie projection works with DLP projectors, but not with standard LCD projectors.


Here is a fascinating history of stereographic imaging from one of its participants.

Here is a teardown and repair page for CrystalEyes units.
Here are some comparisons of different brands of shutter glasses.