3D glasses and other 3D display devices


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Color filter glasses

Color filter glasses were one of the oldest 3D glasses. The system works so that both eyes have a different color filter in front of them. This causes that left eye can only see few colors and right eye some other colors. When the led eye's colors are used to draw the emage which it should see and same is used for right eye, the combined image can be viewed with suitable glasses in 3D. The most common color combinations are red+green and blue+green. The color filtering limits that there are only few possible colors in use in th epicture so the images made using this method are not very nice to look.
Color filter glasses have been used in 3D movies and some early computer games. The advantage of this method is that the 3D material can be stored to any standard color video media and viewed with normal display devices as long as you wear the right color filter glasses. The galsses are very inexpensive beacuse you only need very cheap plastic filters for them. You can even make your own glasses from piece of cardboard and suitable filters (standard lighting GEL numbers R26 and R83 should be quite suitable for red+green glasses).
This technique causes colors in the image to be compromised because you have too many different colros in different eyes. Practically you loose almost all your color, so you can see objects coming out of the screen but they are gray. The colors also create some eyestrain and distortion.


Polarizing glasses

This method is usually used with projection displays when 3D material needs to be displayed. Every viewer has to wear special glasses which have two polarizing lenses which have their polarization directions adjusted to be 90 degrees different. This makes is possible that left eye sees it's picture without problems but everything ment to right eye (sent out at different polarization) seems to be black. Same applies also to right eye.
The material which has to be shown is typically projected using two projectors (film projector, slide projector or video projector) which each have polarizing lenses in front of them (adjusted to meet the polarization directions of the glasses). The projection surface must be specially made so that it does not do any harm to the polarization (many traditional projection surface materials are not suitable, silver stripe screen is recommended). The advantage of this method is that the pictures can be in full color and the viewing glasses are still quite inexpensive.

LCD shutter glass method

In the LCD shutter glass 3D display, the left and right images are alternated rapidly on the monitor screen. When the viewer looks at the screen through shuttering eyewear, each shutter is synchronized to occlude the unwanted image and transmit the wanted image. Thus each eye sees only its appropriate perspective view. The left eye sees only the left view, and the right eye only the right view.
A field-sequential 3D (stereoscopic) video signal is a normal video signal (PAL, NTSC or SECAM) which has been specially recorded with left and right images stored on the even and odd fields of the video signal. The 3D video signal is usually viewed while wearing a pair of LCD shutter glasses which only allow the left eye to see left images and the right eye to see right images.
If the images (the term "fields" is often used for video and computer graphics) are refreshed (changed or written) fast enough (often at twice the rate of the planar display), the result is a flickerless stereoscopic image. This kind of a display is called a field-sequential stereoscopic display.


Flicker

Another common scapegoat for inadequate hardware, software, and lack of stereo training is flicker, which is most noticeable in standard frequency (e.g. 60 Hz) field sequential systems. It varies with many factors, especially screen brightness, screen size and room illumination. The image may still flicker even at 120 Hz screen refresh if the image is not updated in the proper way. Decreasing the level of ambient illumination in the room can reduce the room flicker to imperceptible levels. Reducing screen luminosity with brightness and contrast controls will reduce image flicker to low or imperceptible levels.

How glasses are controlled

There have been many methods for controlling the LC shutter glasses. The liquid crystal shutter elements (size usually 3/4"x1") itself have to be driven using AC voltage, because DC would destroy the liquid crystals. The driving signals are typically around 3-8V and frequency is usually fre hundred Hz. The shutter elements are usually designed so that when no voltage is connected to them you can see through them and when you apply the AC control voltage those elements become black.