Perspective is everything and, when it comes to three-dimensional imaging, it's the only thing. Human vision has depth because of the placement of our eyes and the processing matrix in our brains that decode two flat images into a three-dimensional view. Cameras have to accomplish both image capture and image decoding to successful render three-dimensional images.
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Human eyes are about two and one-half inches apart, on average, and the combination of slightly different perspectives is interpreted by the brain into three-dimensional space. The challenges inherent in 3-D photography are twofold. A camera must first have a way of photographing two images of one scene with slightly different perspectives. Then, since a photograph, video or movie frame is a two-dimensional representation, the 3-D system must deliver each image of a stereo pair separately to both the left and right eyes of the person viewing.
The first attempts at creating 3-D photos required the photographer to take two separate photographs of the same scene, shifting the camera slightly between exposures. Once the viability of the process was established, stereo cameras were built, with two lenses capable of capturing two images simultaneously, or the stereo photographer would arrange two cameras. Viewing was done using lenticular separation. The stereoscope had two lenses that aided focusing left and right eyes separately, creating the 3-D effect.
Contemporary 3-D Cameras
Specialty cameras with two lenses and two image sensors are available for simultaneous exposure of a stereo pair. Due to the additional hardware and limited demand, these cameras are more expensive than single-lens cameras of similar quality and features. Panasonic and Fujifilm market double-lens, 3-D cameras. A recent trend adds 3-D assist capabilities to conventional cameras. Some Nikon and Sony cameras, for example, allow the photographer to shoot one scene, then shift the camera assisted by a translucent image on the camera display. After the subject is aligned, the camera exposes the second image, using the same exposure and focus.
Decoding and Viewing
Today's 3-D cameras capture the images and do not perform any of the decoding functions needed to view the photos three-dimensionally. Passive decoding technology uses either anaglyphic viewing -- the red-and-cyan lensed glasses -- or polarized viewing, which uses gray lenses with different polarizing directions. Active decoding viewing uses battery-powered glasses to sync polarized images with a 3-D television. Viewing 3-D TV without glasses can be accomplished through the use of lenticular screens, but the field of view for these TVs is limited, and the lenticular screen reduces image resolution.