Autostereoscopic 3D LCD Monitors
Computer users have been able to get real 3D images for quite some time, often by using clunky shutter glasses with a CRT monitor. However, now that LCD monitors are standard it is no longer possible to use relatively cheap 3D glasses to provide a real 3D image.
The most popular form of 3D LCD technology is called "autostereoscopic technology" and is able to provide a 3D image without any glasses. This technology works by diverting each column of pixels to an individual eye, essentially halving the vertical resolution but providing a unique image to each eye. By displaying a correctly rendered image on the monitor it is then possible to trick the brain into believing that the two 2D images are a single 3D scene.
There are two ways of directing the light to each eye, either by using a "parallax barrier" or a "lenticular lens". The two diagrams below illustrate how the light from left and right pixel columns reaches the eye.
Parallax Barrier
In the parallax barrier a mask is placed over the LCD display which directs light from alternate pixel columns to each eye. Parallax barrier displays allow instant switching between 2D and 3D modes as the light barrier is constructed from a layer of liquid crystal which can become completely transparent when current is passed across, allowing the LCD to function as a conventional 2D display.
Lenticular Lens
In the lenticular lens, an array of cylindrical lenses directs light from alternate pixel columns to a defined viewing zone, allowing each eye to receive a different image at an optimum distance. 
3D Viewing Position
Of course, these methods produce zones in which the viewer can see a 3D image and the head must be correctly aligned within these zones to comfortably view the scene. If the head is located outside of these zones then both image streams will reach each eye or the viewing positions will be inverted, both of which will cause comfort problems.
This limits most low/medium end monitors as it restricts the head movement to within a small viewing region to achieve the full 3D effect. High end monitors can use different methods of eye/head tracking to adjust a parallax barrier, altering the viewing zones to follow the eye positions. This provides a seamless 3D viewing experience from an LCD monitor, without any external equipment.
Source: ReviewSpring
