Random-dot stereogram

Random-dot stereogram (RDS) is stereo pair of images of random dots which when viewed with the aid of a stereoscope, or with the eyes focused on a point in front of or behind the images, produces a sensation of depth, with objects appearing to be in front of or behind the display level.

The random-dot stereogram technique, known since 1919, was much used by Dr. Béla Julesz and it, along with additional research, lead to publication of an influential book detailing his theories and work on the basis of human stereo vision entitled Foundations of Cyclopean Perception.

Later concepts, involving single images, not necessarily consisting of random dots, and more well known to the general public, are known as autostereograms.

Dr. Julesz emigrated from Hungary to the United States following the 1956 Soviet invasion. After his arrival, he found himself working at Bell Labs. One of his projects involved detecting patterns in the output of random number generators. Dr. Julesz decided to try mapping the numbers into images and using the pattern-detecting capabilities of the human brain to look for a lack of randomness.

In 1840, Sir Charles Wheatstone developed the stereoscope. Using the stereoscope, two photographs, taken a small horizontal distance apart, could be viewed with the objects in the scene appearing to be 3-dimensional. Over 100 years later, Dr. Julesz noticed that two identical random images similar to what he had produced in his previously mentioned project, when viewed through a stereoscope, appeared as if they were projected onto a uniform flat surface. He experimented with the image pair by shifting a square in the center of one of the images by a small amount. When this pair was viewed through the stereoscope, however, the square appeared to rise out from the page.

Though interesting on its own as a technique for producing sensations of depth in printed images, the discovery also had implications in cognitive science and the study of perception.

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