All About SIRDS
(Single Image Random Dot Stereograms)
Most people have seen or are familiar with SIRDS or Single Image Random Dot Stereograms. Think of those magic eye books that you hold close to your face and slowly pull back for the 3D image. The images used are composed of many tiny dots that when viewed correctly reveals a three dimensional image perceived by the brain. The human brain overcomes the series of dots through the use of vergence and focusing. The most basic form of SIRDS, also called autostereograms, consists of repeating patterns in a horizontal arrangement and when proper vergence viewing is applied an object or scene appears above or below the original image. Autostereograms are viewed without the use of a stereoscope; a stereoscope allows each eye to receive different images and reconstruct them internally to form a three dimensional image. It is comprised of two eyeglasses, and by reflection and refaction the photos are superimposed, appearing as one to the user.
The original stereoscope was developed by Charles Wheatstone in 1838 in an effort to understand the mechanisms of depth perception in humans. He separated an image into two different mirrored images and placed them on an apparatus to demonstrate that the eyes can perceive three dimensions from two dimensional images. In the nineteen fifties work at Bell Laboratories led to the discovery that depth perception is not a function of the eyes but rather interpreted by complex neurological mechanisms in the brain. The individuals working at Bell labs noticed the effect when scanning photos of camouflaged aerial photographs of military installations and outposts.
The main use of SIRDS is in the understanding of how the brain perceives light, motion, three dimensional depth perception and how the eyes communicate to the brain via nerves. The concept is that each eye can see a different image and that the brain reconstructs the two images into a single frame. This allows for research and tests to be set up and performed to measure the perception of the brain and how it communicates to other portions for depiction and understanding. While the initial use was for research and information, which is still being carried out, SIRDS soon found a following of commercially available "puzzles" and eye games purely for fun.
Perhaps the most popular of these puzzle books was the Magic Eye books of the nineteen nineties. In addition the SIRDS are used in psychological tests and memory tests in some areas of visual psychology. The puzzles have gotten more and more intricate as more individuals working with SIRDS develop new algorithms for producing the random dots for use in a variety of applications. Some of these algorithms actually remove the color from the image when viewed at the correct vergence. Through the use of SIRDS scientists and researchers have discovered and documented the processes of stereopsis or the process of depth perception without the information from external sources such as colors, shades and a background which were once thought to be the foundations of depth perception.
SIRDS still play a role in research although most people interact with them in a purely entertainment setting. They serve to improve visual effects in movies and video games as well as serving the military and scientific communities researching stealth and camouflage. Animated SIRDS are now available for viewing and are proving to be an invaluable asset to the research of human neurology.