There is a fourth approach to 3D glasses that works as follows.

Each lens is like a double glazed window filled with liquid crystal that can be changed quickly from transparent to opaque. Alternate frames of the film show slightly different perspectives, so that all the odd numbered frames are suitable for viewing with the left eye and all even numbered frames are for the right eye (or vice versa.)

When viewing the display the left and right lenses are alternately switched on and off so that the eyes only ever get to see the appropriate frames. Due to the phenomenon of persistence of vision, the brain can be convinced that both eyes are receiving an uninterrupted view and so it is tricked into perceiving the alternate two dimensional images as a single three dimensional view.

Because this technique relies on showing alternating perspectives it is most suited to use in film or computer screens as opposed to printed media.