Traditional three dimensional computer displays require the viewer to wear glasses of some sort to ensure each eye receives a different image. Some rely on different colours, others flicker the two images quickly while also blocking the view to each eye alternately. A parallax barrier allows normal viewing of a 3D display without the need for glasses.
The device, filed for patent by Sanyo Electric Co. on December 8, 1997, is a set of opaque vertical stripes, situated some way behind the display plane of an LCD display. The backlight source is the other side of the barrier.
The barrier ensures that light reaching the left eye goes through a different set of pixels on the display screen from that reaching the right eye - the angle subtended by the eyes at the screen is crucial, so the distance between the viewer and the screen may have to be adjusted according to to the distance between the viewer's eyes.
In its simplest form, each alternate column of pixels corresponds to a different eye. Two adjacent columns come from the same gap in the parallax barrier, but to different eyes.
Sharp have since developed a switchable 2D/3D display, where the parallax barrier is also an LCD display. This allows a normal mode of viewing where all pixels are visible to both eyes.