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an image that creates the illusion that the picture viewed is three-dimensional, or spatial. When the two images of a stereopair are viewed separately by the right and left eyes, they blend together in the perception of the viewer to form a single visual image. In order for this to occur, the images must be projected in such a way that the retina of each eye receives the correct image. A stereoscope is an example of a device that serves this purpose.
Each image of a stereopair can be colored differently; for instance, the right image may be red and the left image green. Both images can then be combined and superimposed by printing or by projecting onto a screen. If such a combined image is viewed through colored eyeglasses, the left eye will see through a red filter a black silhouette of the green image, and the right eye will see through a green filter a dark silhouette of the red image only. This method of printing and projecting stereoscopic images is called the anaglyphic method.
Linearly polarized light is also used for viewing the coincident images of a stereopair. The polarization planes of the light for the right and left images are mutually perpendicular. In this case, both images are printed on correspondingly oriented polarized film, and the stereoscopic image is viewed through polarized eyeglasses.
Raster optics, such as those used in the integral Lippmann process and related methods, are used to produce three-dimensional images that can be viewed without eyeglasses from various viewing positions. The development of holography has made it possible to obtain fully three-dimensional images that are perceived as stereoscopic images from any viewing position or as the observer moves.