Human beings view the world stereoscopically. It means that the two eyes see slightly different images since they are separated by about six centimetres ( two and a half inches ). In 2D, there is a single flat image which means the two eyes see the same picture on the screen. In 3D image, one has to present a slightly different image to each eye.

Glass-based system: It works by having two lenses that each polarise the light in slightly different directions.

Red-and-Green Lenses:  In glass-based system, the display has two simultaneous images, each with different polarisation. In red-and-green system, the images have red/green outlines.

Glass-free System: This is the current system. It uses thin lenses called lenticules or parallax barriers that send an image towards each eye.The 3D effect is limited and can be perceived only when the viewer is positioned in the narrow zone, so that the correct eye gets the correct image.

Princess Lei-style Holography: Here the characters leap out from the screen as Princess Leia did in that scene from Star Wars. This cannot be used for images displayed at a normal video rate, as the demands in pixel density are just too great.

Defractive Optics

These images can be watched from multiple angles even if the device such as cell-phones, tablets and watches are tilted. Other 3D technology use horizontal parallax—you see the 3D when you move your head left and right. In the defractive optics, you do full-parallax. The new  ‘auto-stereoscopic multi view’ display uses a back light where the surface has been etched with tiny refractors. Each of these microscopic deflectors sends individual points of light in different directions. These individual pixels, put together, comprise different images sent to each eye ball.