User:Mmdoogie/RDS

Random Dot Stereograms are pairs of images of random dots which when viewed with the aid of a stereoscope, or with the eyes focused on a point behind the images, produce a sensation of depth, with objects appearing to be in front of or behind the actual images.

The Random Dot Stereogram (RDS) technique was invented 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.

Development
Dr. Julesz emigrated from Hungary to the United States following the 1956 Soviet invasion. After his arrival, he found himself working at Bell Labs, alongside many other great names in mathematics. 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.

Implications
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.

The random dot stereogram provided insight on how stereo vision is processed by the human brain. According to Ralph Siegel, Dr. Julesz had "unambiguously demonstrated that stereoscopic depth could be computed in the absence of any identifiable objects, in the absence of any perspective, in the absence of any cues available to either eye alone."

Dr. Julesz termed this 'cyclopean perception' based on his theory that the brain forms a single-image mental model of a scene, as a Cyclops would, but with depth information added, despite receiving two disparate images from the eyes. His theories and work are detailed in his 1971 book.

Further Development
The name 'random dot stereogram' specifically refers to pairs of images based on random dots. Additional work by Christopher Tyler and Maureen Clarke led to encoding the same data into a single image which did not require a stereoscope for viewing. These are known as Single Image Random Dot Stereograms (SIRDS), or Random Dot Autostereograms.

Replacing the random dot base pattern with an image or texture gives the form that made the Single Image Stereogram known to the general public, through the Magic Eye series of books.

Illustrated Example
The process used to develop the first Random Dot Stereogram is illustrated below.

1. Create an image of suitable size. Fill it with random dots. Duplicate the image.



2. Select a region in one image.



3. Shift this region horizontally by a small amount. The stereogram is complete.



To view the stereogram, focus on a point behind the image by a small amount until the two images "snap" together. Note that viewing the identical images from step 2 in this manner will work, but the whole area will appear at the same depth. The shifted region produces the binocular disparity necessary to give a sensation of depth. Different shifts correspond to different depths.