Each half of the Dolby color wheel has a different filter to separate the left and right images in a stereo pair. Image courtesy of JDSU.
Light travels in waves and the distance between the crests or valleys is called the wavelength and can be specified
in nanometers (nm). Filters can be designed to pass or block any specific wavelengths and that's what Dolby 3D glasses do.
Click to see an animation of how all colors can be created from red, green and blue.
Dolby 3D uses a technology based on spectral separation that’s a sophisticated form of anaglyphs. If the color spectrum could be imagined as a loaf of bread, an anaglyph would be like cutting two thick slices out of the loaf—one for the left eye and one for the right. Dolby 3D would be like slicing the loaf into 6 finer slices.
To separate these slices from the loaf, a color wheel in front of the projector spins so it is synchronized with the movie frames being flashed on the screen one after the other at 144 frames per second. The spinning wheel is divided in half with each half having a different color filter that passes only selected
wavelengths. For example:
- The filter for the left eye passes Red 629nm (nanometers), Green 532nm, and Blue 446nm.
- The filter for the right eye passes Red 615nm, Green 518nm, and Blue 432nm.
Viewers wear passive glasses with differently colored filters in each lens so each eye sees only the image it’s meant to see. The filter over the left eye passes the longer wavelengths of red, green and blue and the filter over the right eye passes the shorter wavelengths of the same colors.
Dolby glasses have a red/cyan tinge to them but allow different parts of the red, green and blue spectrum to pass to each eye.
The lenses are curved to reduce ghosting.
This finer slicing of the spectrum lets you see full color images because each eye sees some of the spectrum for the primary colors—red, green and blue—and these three colors can be mixed to form any other color in the spectrum. Both eyes see a full spectrum of color, but at slightly different wavelengths. Since entire color channels are not deleted—as they are in anaglyphs—only a few frequency regions of color are lost instead of whole color channels.
The filters in each lens are made up of 70–80 layers of titanium oxide or silicon oxide, each with a different index of refraction. They either reflect or allow light to pass depending on its wavelengths. The glasses are designed with curved lenses to eliminate ghosting—when one eye sees an image intended for the other eye.
A color wheel in front of a Dolby 3D projector lets through selected wavelengths in the red, green and blue channels and blocks the rest. Although both eyes see red, green and blue, the wavelengths for each eye are different so a viewer’s left eye sees the left image and the other eye see the right.
Dolby 3D technology projects 3D images onto standard screens—avoiding the expense of a silver screen required by polarization—the most popular technology used in cinemas (and which will be discussed shortly). It´s also possible to use the same system to project 2D movies by just removing the color wheel from in front of the projector.
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Dolby's technology is technically called "wavelength multiplier visualization." This is a great phase to use in Web searches because it is so specific.