Displaying 3D Using Glasses

A 3D camera at the Ice Hockey World Championships 2008 in Canada - the photograph itself was taken as a 3D picture using the red-green process.

The classic 3D process, tried out in movie theaters in the 50s, uses glasses with two different-colored lenses. The pictures for the left and right eyes appear in different colors, which the corresponding lenses then separate.

Advantages:
Possible with all color-screens; works for projection and in print.

Disadvantages:
Significantly worse color-reproduction; irritating result. Recently, however, also possible with red and cyan as direct complementary colors, allowing better separation of the two channels.

The Colorcode process uses a pair of glasses with one dark-blue and one amber lens. This allows one eye to see an almost correct color-picture while the other eye perceives the image's depth.

The combination of these two into a 3D impression works better than with red-green glasses, but, depending on the viewer, the brightness difference limits the effect to a lesser or greater extent.

Advantages:
Possible with all color-screens; works for projection and in print; good color reproduction.

Disadvantages:
Slightly poorer 3D impression; sometimes irritating because of the pronounced darkening of one eye.

A 3D picture in the Colorcode process has the advantage that the colors are better preserved than with red-green encoding.

German firm Infitec developed this process, which uses narrowband color-filters, and which Dolby now applies in 3D movie theaters. The process defines a specific band within each color, so that both eyes receive red, green, and blue. The images are projected alternately by DLP projectors, but the method is also possible with other, specially prepared projectors.

Advantages:
Relatively easy to implement with three-chip DLP-projectors; good picture quality.

Disadvantages:
Glasses are expensive, tricky to achieve using conventional screens.

This system uses vertical and horizontal polarizers to filter light oscillating in the respective directions, and therefore to direct the two separate signals to the viewer's eyes. This can work using two screens (combined into one image by a mirror system), two projectors (shining onto one screen), or a single projector producing the polarized images alternating one after another (see alternating pictures, below). Another method uses filters within LCD screens, taking advantage of the polarizing filters that these screens require in the first place; this results in halved resolution.

Advantages:
Cheap glasses, decent picture quality.

Disadvantages:
Ghost images if you tilt your head; requires a "silver screen" for projection, since the polarization of the light is otherwise interrupted.

These separate the images according to clockwise and counterclockwise polarization - commonly used in digital movie theaters with installations by the firm RealD. Otherwise uses exactly the same principal as linear polarization (above).

Advantages:
Cheap glasses, high quality.

Disadvantage:
Requires image editing and special projection screen.

If a screen displays different images one after the other, you can use glasses that open and close their left and right lenses alternately to achieve accurate 3D representation. This requires double the picture refresh rate (therefore at least twice 50 Hertz) - at slower rates, the picture begins to flicker.

The firm Xpand uses this system in digital movie theaters, and Samsung and Panasonic have demonstrated it on plasma displays. The DLP TVs that support 3D - offered in the USA by Samsung and Mitsubishi - use alternating pictures and shutter glasses.

Advantage:
Excellent 3D effect with excellent picture quality.

Disadvantage:
Costly screens and glasses.

One alternating-picture version uses the interlaced process of TV standards, together with the corresponding display-method on tube screens. This system allocates one interlaced frame to one eye, the next frame to the other, and so on. Corresponding images can of course only be viewed using the appropriate shutter glasses. Cannot be used with 100-Hertz TVs, since the signal frequency and display frequency would no longer match - the method also won't work with flat-panel TVs or digital projectors.

Advantage:
Works using existing video sources such as VHS or DVD, as well as with tube TVs with no picture memory.

Disadvantage:
Pronounced flicker due to halved picture refresh rate (25 or 30 Hertz); not possible using modern screens.

If images appear alternately in different color variants, there's no longer a need for expensive, technically sensitive shutter-glasses. This method can work with DLP movie-theater projectors, which have no problem doubling the frame rate. The picture quality depends on the filter technology - movie theaters use wavelength multiplexing (see above).

Advantages:
Easy to implement with digital projectors; generally good picture quality.

Disadvantage:
Slight color distortion is possible.

Instead of shutter glasses, it's also possible to use polarized glasses with alternately polarized projected images. This is frequently used in digital movie theaters (RealD, see section 2). The method can use a variety of polarization processes.

Advantages:
Cheap glasses, good picture quality.

Disadvantage:
Requires image editing and special projection screen.

The so-called Pulfrich process delays the image in one eye by using a darkened lens. During sideways motion in the picture, the brain then combines two images that produce the impression of 3D vision if the camera moves in the direction defined by the glasses; in general, the camera must move from right to left past or around objects.

Advantages:
Possible with all types of video or film cameras; can display on all screens; cheap glasses.

Disadvantages:
Only works with sideways motion of the camera or of objects in the picture; strong brightness difference between the lenses is irritating.

Using special optics, it's possible to produce an image within a pair of glasses, but which appears to hover a few meters in front of the viewer. Since this already requires separate units for each eye, this type of glasses seems predestined for displaying 3D. The mini-displays mostly use LCoS or LCD technology like that used in a camera's viewfinder.

Advantages:
Excellent picture quality if using an appropriately high-resolution display device; no disturbances from external influences.

Disadvantages:
Only for one person; takes some getting used to.

Passive glasses are cheap. Pictured here: Pulfrich, polarizer, and red-cyan versions.