What is a 3D image ?
The things in the world can be calculated in 3 dimensions. We enjoy the real world with two eyes and each of it is in a different location, then each sees a slightly different perspective of what we are looking at.
Our brain can combines the view from each eye into a single picture, and the combined image includes the three dimensions of an object.
if somebody sees a die, then each eye sees a slightly different view of this die.
To display the die in 3D, you need to display a separate and different image to each eye. The 3D glasses will be necessary to ensure that each eye only sees the image meant for that eye.
3D Video systems
3D video systems are offering a duplication of the world experience by giving to each eye a unique version of the video. By projecting a separate image for each eye, a 3D image is created. The objects in a 3D video can be in front of or behind the screen. To view 3D video, the display technology and the 3D glasses are capable to give to the left eye only the video meant for this left eye, and same for the right eye. Plenty of different technologies are designed to accomplish the 3D viewing.
The Anaglyphic method
The most popular 3D glasses are the one with red & blue lens as this system was used in the past for many 3-D movies and 3D effects. These glasses use the anaglyphic method of displaying a 3D image.
Anaglyph image is made by using color filters to remove a part of the visible color spectrum from the image meant for each eye which only sees the image that contains the portion of the color spectrum not filtered out by the lens.
The Polarized technology
The light travels in waves which can be watched vertically or horizontally by using different polarizing filters. When the light goes through a polarizing filter which is horizontal, it can can pass through but it will be blocked by a vertically aligned polarizing filter.
This technology is done by changing the polarization of the light emitted from each pixel to the desired orientation for each eye : the resolution provided by polarized displays to each eye is half of the full display resolution.
The Alternate Frame solution
Some of the latest 3D HD televisions are capable to displaying 3D video with separate left and right-eye pictures in an alternating sequence. To avoid a flicker effect, it is necessary to use a refresh rate of 200 Hz for example : then a 200 Hz 3D TV will display a full resolution frame for left eye for a 200th of a second, followed by a full resolution frame for the other eye (right) for the next 200th of a second. The result is each eye will see 100 frames per second, but for less than half the time that the video is playing.
This technology is known by the “active shutter” glasses for viewing 3D video. They are made with liquid crystal lenses in front of each eye and received an infrared synchronization signal from a base station to synchronize the glasses to the display.