The latest blockbuster films from Hollywood all seem to be shown in the cinemas in 3D, and many electronics manufacturers have brought 3D-capable televisions, cameras, and phones onto the consumer market.
But how does 3D work? How can we look at a flat image and see a moving solid object?
There are a few different methods to accomplish this, but they all revolve around the same principle - providing each eye with a separate image. This technique is known as stereoscopy.
Our brains interpret the slightly different images from each eye to create the 3D depth we see. By controlling how these images differ, we can create the illusion of depth in a flat image.
Figure 1. Samsung explain how their active 3D televisions work.
Anaglyph 3D is the oldest method of creating 3D images and film. The two images are in two different colours, and the viewer uses glasses with different colour filters on each eye.
This method is very easy to achieve, and requires no special equipment to display. There is one major drawback, however - viewers without the correct coloured glasses will see a strange, distorted image.
Polarization is the 3D method used currently in cinemas and other large-format displays. the image is displayed using two synced projectors, showing the left and right images. The two images are polarized - either with clockwise and anti-clockwise circular polarization, or with perpendicular linear polarization.
The glasses worn by the viewer have matching polarizations in the lens, so that each eye receives the correct image.
This system is very effective for users wearing glasses. Viewing without glasses still results in distortion, as both images are visible - however, the colour distortion from anaglyph 3D is not present.
Polarization 3D is not easily transferable to other types of display, like LCD screens, as they already feature polarizing filters.
Active Shutter 3D
This method is used in many commercial 3D televisions and projectors. Left and right images are displayed in alternate videos frames. Glasses containing active shutters then simply block each eye alternately, synchronized with the display via an infrared signal.
The frame rate for the video obviously needs to be twice as fast as normal. When combined with the need for active glasses, this makes the overall cost of active 3D systems quite high.
However, because of the high frame rate, viewers without 3D glasses can still watch without distortion - the human eye is not fast enough to detect the difference between the frames when they are changing that quickly. This is a major advantage of active shutter 3D for home use, where the number of 3D glasses may be limited.
Figure 2. A "true 3D" volumetric display.
Autostereoscopic and Volumetric 3D
There have also been advances in displaying 3D images and content without the need for glasses. This is known as autostereoscopic 3D, and thus far it has quite limited applications. The 3D images will only display properly when the display is set for a particular viewing position.
Devices like the Nintendo 3DS, a portable gaming system, can count on just having one user at a time, in a relatively consistent position relative to the screen. For larger displays such as televisions, however, where multiple viewers are likely, this technology is not currently workable.
Prototype devices have also been developed which are capable of projecting an actual 3D image - these are called volumetric displays. The most common techniques use projection onto a spinning mirror to achieve this. The technology is difficult to scale, however, and is currently at the demonstration stage at best.
Recently, there has been much discussion about whether 3D at the movies and in TVs will become more and more commonplace, or whether it is a short-term fad, which will go out of fashion once the novelty wears off.
Irrespective of its consumer appeal, 3D technology has important applications in more technical fields. 3D displays are very useful in CAD systems, and will become more so as 3D printing becomes more and more affordable and ubiquitous.
3D imaging is also an important part of many quality control and quality assurance processes in manufacturing. 3D displays are useful for visualizing the 3D structures of molecules, and structures in microscopic biological systems or novel materials.
Although it may not be the home-cinema hit that many manufacturers are hoping for, 3D technology will always be useful, and advances in volumetric and holographic displays will only increase the number of possible applications.
References and Further Reading
- "3-D Filmmakers: Conversations with Creators of Stereoscopic Motion Pictures" - Ray Zone.
- "Stereoscopic Cinema and the Origins of 3-D Film, 1838-1952" - Ray Zone
- "How Does 3D Work?" NASA STEREO Learning Center
- "Active 3D vs. Passive 3D" - PC World