Stereoscopy is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word stereoscopy derives from Greek στερεός, meaning firm, solid, any stereoscopic image is called a stereogram. Originally, stereogram referred to a pair of images which could be viewed using a stereoscope. Most stereoscopic methods present two offset images separately to the left and right eye of the viewer and these two-dimensional images are then combined in the brain to give the perception of 3D depth. Stereoscopy creates the illusion of depth from given two-dimensional images. One of the functions that occur within the brain as it interprets what the eyes see is assessing the relative distances of objects from the viewer, the two images are then combined in the brain to give the perception of depth. Although the term 3D is ubiquitously used, the presentation of dual 2D images is distinctly different from displaying an image in three full dimensions. The most notable difference is that, in the case of 3D displays, holographic displays and volumetric display do not have this limitation. Just as it is not possible to recreate a full 3-dimensional sound field with just two speakers, it is an overstatement to call dual 2D images 3D. The accurate term stereoscopic is more cumbersome than the common misnomer 3D, although most stereoscopic displays do not qualify as real 3D display, all real 3D displays are also stereoscopic displays because they meet the lower criteria also. Most 3D displays use this method to convey images. It was first invented by Sir Charles Wheatstone in 1838, but if it be required to obtain the most faithful resemblances of real objects, shadowing and colouring may properly be employed to heighten the effects. Flowers, crystals, busts, vases, instruments of various kinds, Stereoscopy is used in photogrammetry and also for entertainment through the production of stereograms. Stereoscopy is useful in viewing images rendered from large data sets such as are produced by experimental data. Modern industrial three-dimensional photography may use 3D scanners to detect and record three-dimensional information, the three-dimensional depth information can be reconstructed from two images using a computer by correlating the pixels in the left and right images. Solving the Correspondence problem in the field of Computer Vision aims to create meaningful depth information from two images, anatomically, there are 3 levels of binocular vision required to view stereo images, Simultaneous perception Fusion Stereopsis These functions develop in early childhood. Some people who have strabismus disrupt the development of stereopsis, however orthoptics treatment can be used to improve binocular vision, a persons stereoacuity determines the minimum image disparity they can perceive as depth. It is believed that approximately 12% of people are unable to properly see 3D images, according to another experiment up to 30% of people have very weak stereoscopic vision preventing them from depth perception based on stereo disparity
Pocket stereoscope with original test image. Used by military to examine stereoscopic pairs of aerial photographs.
View of Boston, c. 1860; an early stereoscopic card for viewing a scene from nature
A company of ladies looking at stereoscopic views, painting by Jacob Spoel, before 1868. An early depiction of people using a stereoscope.