Editing Autostereogram (section)

===Simple wallpaper===
[[Image:Stereogram Tut Clean.png|thumb|350px|This is an example of a wallpaper with repeated horizontal patterns. Each pattern is repeated exactly every 140 pixels. The illusion of the pictures lying on a flat surface (a plane) further back is created by the brain. Non-repeating patterns such as arrows and words, on the other hand, appear on the plane where this text lies.]]
[[Stereopsis]], or stereo vision, is the visual blending of two similar but not identical [[real image|image]]s into one, with resulting [[visual perception]] of [[solid]]ity and [[depth perception|depth]].<ref>Cassin, B. and Solomon, S. (1990). ''Dictionary of Eye Terminology'', {{page needed|date=October 2012}}. Gainesville, Florida: Triad Publishing Company. {{ISBN|978-0-937404-33-1}}</ref><ref>{{Cite report |url=http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=940788 |title=Computational reconstruction of the mechanisms of human stereopsis |last=Tyler |first=Christopher W. |last2=Barghout |first2=Lauren |date=1994-03-17 |doi=10.1117/12.171143 |pages=52–68 |last3=Kontsevich |first3=Leonid L.|url-access=subscription }}</ref> In the human brain, stereopsis results from complex mechanisms that form a three-dimensional impression by matching each point (or set of points) in one eye's view with the equivalent point (or set of points) in the other eye's view. Using [[binocular disparity]], the brain derives the points' positions in the otherwise inscrutable ''z''-axis (depth).

When the brain is presented with a repeating pattern like [[wallpaper]], it has difficulty matching the two eyes' views accurately. By looking at a [[Horizontal plane|horizontally]] repeating pattern, but converging the two eyes at a point behind the pattern, it is possible to trick the brain into matching one element of the pattern, as seen by the left eye, with another (similar looking) element, beside the first, as seen by the right eye. With the typical [[#wall-eyed-viewing|wall-eyed viewing]], this gives the illusion of a plane bearing the same pattern but located behind the real wall. The distance at which this plane lies behind the wall depends only on the spacing between identical elements.<ref name="kinsman">Andrew A. Kinsman (1992). ''Random Dot Stereograms'', {{page needed|date=October 2012}}. Rochester: Kinsman Physics. {{ISBN|0-9630142-1-8}}.</ref>

Autostereograms use this dependence of depth on spacing to create three-dimensional images. If, over some area of the picture, the pattern is repeated at smaller distances, that area will appear closer than the background plane. If the distance of repeats is longer over some area, then that area will appear more distant (like a hole in the plane).

[[Image:Stereogram Tut Simple.png|thumb|350px|This autostereogram displays patterns on three different planes by repeating the patterns at different spacings. ([[Image:Stereogram guide parallel.png|10px]])]]
People who have never been able to perceive 3D shapes hidden within an autostereogram find it hard to understand remarks such as, "the 3D image will just pop out of the background, after you stare at the picture long enough", or "the 3D objects will just emerge from the background". It helps to illustrate how 3D images "emerge" from the background from a second viewer's perspective. If the virtual 3D objects reconstructed by the autostereogram viewer's brain were real objects, a second viewer observing the scene from the side would see these objects floating in the air above the background image.

The 3D effects in the example autostereogram are created by repeating the tiger rider icons every 140 [[pixel]]s on the background plane, the shark rider icons every 130 pixels on the second plane, and the tiger icons every 120 pixels on the highest plane. The closer a set of icons are packed horizontally, the higher they are lifted from the background plane. This repeat distance is referred to as the depth or ''z''-axis value of a particular pattern in the autostereogram. The depth value is also known as [[Z-buffer]] value.

{| border="0"
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| align="center" | [[Image:Stereogram Tut Side View.png|thumb|270px|This picture illustrates how 3D shapes from an autostereogram "emerge" from the background plane, when the autostereogram is viewed with proper eye divergence.]]
| align="center" | [[Image:Stereogram Tut Width.png|thumb|270px|Depth or ''z''-axis values are proportional to pixel shifts in the autostereogram.]]
|}
The brain is capable of almost instantly matching hundreds of patterns repeated at different intervals in order to recreate correct depth information for each pattern. An autostereogram may contain some 50 tigers of varying size, repeated at different intervals against a complex, repeated background. Yet, despite the apparent chaotic arrangement of patterns, the brain is able to place every tiger icon at its proper depth.{{POV statement|date=October 2012|1=The article is insulting towards those of us who can't see the damn things}}

{| border="0"
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| align="center" | [[Image:Stereogram Tut Highlight.png|thumb|260px|The brain can place every tiger icon on its proper depth plane. ([[Image:Stereogram guide parallel.png|10px]])]]
| align="center" | [[Image:Stereogram Tut Highlight Side.png|thumb|270px|This image illustrates how an autostereogram is perceived by a viewer]]{{clear}}
|}