Stereoscopic displays require that users wear some form of glasses to separate the left and right images so that each image is seen only by the appropriate eye. This approach needs the two images to be encoded by the display so that the glasses can filter the left and right views correctly. There are four main approaches:
Left and right images are transmitted from the display alternately in time. The glasses are shutters which switch in time with the transmission sequence so that light is allowed to an eye only when the display is showing the appropriate image. When the shutters switch fast enough (above 60Hz per eye) the flicker of the shutters is not normally visible.
Either linear or circular polarization can be used to encode the two images with differently polarized light. The viewer then wears a pair of lightweight glasses with different filters in each eye that allow through only the appropriate polarization. Linear polarization tends to have the best optical performance, but circular polarization allows viewers more freedom to tilt their heads while watching a display.
Wavelength The traditional anaglyph (red-green) glasses are a basic example of this approach. Two colours are chosen, the left image encoded in one and the right in another. The filters on the glasses match these and the images are seen by the correct eye. Advances in the coding and filters can make these work remarkably well.
More recently designs using carefully designed notch filters in the coding and the glasses allow different full colour images through to each eye.
Spatial Displays which spatially separate the left and right images include head-mounted displays, which provide a separate display in front of each eye. Wheatstone and Brewster style stereoscopes also fall into this category.