A random-dot stereogram (RDS) is stereo pair of images of random dots that, 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 due to stereopsis, with objects appearing to be in front of or behind the display level.
Later concepts, involving single images, not necessarily consisting of random dots, and more well known to the general public, are autostereograms.
Around 1956, Béla Julesz initiated a project at Bell Labs aimed at identifying patterns within the output of random number generators.
He decided to try mapping the numbers into images and using the pattern-detecting capabilities of the human visual system to look for a lack of randomness.
[1] Julesz noticed that two identical random images when viewed through a stereoscope, appeared as if they were projected onto a uniform flat surface.
The discovery of the random dot stereogram was intriguing not just for its ability to create depth sensations in printed images but also for its implications in cognitive science and the study of perception.
The random dot stereogram provided insight on how stereo vision is processed by the human brain.
About 5% of individuals are unable to perceive depth in random-dot stereograms due to various disorders of binocular vision.
The stereoacuity is measured from the patient's ability to identify forms from random dot backgrounds, as presented on several plates or pages of a book.
Additional work by Christopher Tyler and Maureen Clarke led to their inventing single images yielding depth without a stereoscope.