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The process of simulating 3D from 2D sources has always been one of illusion and compromise, and that hasn’t changed a great deal as science has progressed since the first 3D imaging of 1838. The earliest systems provided the stereoscopic illusion by using two images taken from slightly different perspectives to mimic what binocular vision provides the human eye in real time. Each image was then exclusively presented to the appropriate eye using a stereoscope that isolated each eye’s filed of view and adjusted the focal point of the images. The View-Master of the 1940s provides a more contemporary example of this technique in action. A similar effect can be obtained without the stereoscope by using cross-eyed or divergent viewing, but with greater eyestrain and distraction for the viewer.

A somewhat more open and accessible approach based on the same concept involves anaglyph images, where the two offset images used previously are each run through a different color filter (red-blue, for example) and then projected on top of each other. This is then viewed wearing glasses that contain a red filter over one eye and a blue filter over the other, with the brain being appropriately confused into the perception of depth with the merged image. Anaglyph images allowed the use of simple glasses instead of a rigid viewing device, and opened 3D imaging up to more leisurely viewing environments such as a movie theater.

An alternative but similar 3D technology that dates back to about the late 1920s involves offset images filtered with different linear or circular polarized light instead of color. While this technology does not deliver the dream of unassisted 3D viewing it does provide a high degree of depth, color and resolution performance with an acceptable eyewear-based form factor. Although various companies such as Phillips are exploring eyewear-free 3D using pixel-by-pixel lens systems, cost, resolution and viewer positioning issues will likely be limiters for some time to come in many applications.

Alternative Polarization Paths

There are a variety of different functional ways to generate a polarization-based 3D effect.

Most light is unpolarized, with the light waves vibrating in many planes. Fliters can be used to polarize the light linearly across a specific axis by only allowing waves through on that axis—for example on a 90° vertical or horizontal plane. An additional quarter-wave retardation plate can be added to phase shift the polarized light 45° causing the light to rotate left or right in time, creating circular polarized light.