Editing Autostereogram (section)

===3D perception===
[[Depth perception]] results from many monocular and binocular visual clues. For objects relatively close to the eyes, [[binocular vision]] plays an important role in depth perception. Binocular vision allows the brain to create a single [[Cyclopean image]] and to attach a depth level to each point in it.<ref name="julesz"/>

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| [[Image:Stereogram Tut Eye Diagram.png|thumb|left|170px|The two eyes converge on the object of attention.]]
| [[Image:Stereogram Tut Eye View Composite.png|thumb|left|170px|The brain creates a Cyclopean image from the two images received by the two eyes.]]
| [[Image:Stereogram Tut Eye View Depthmap.png|thumb|left|170px|The brain gives each point in the Cyclopean image a depth value, represented here by a grayscale depth map.]]
|}
The brain uses coordinate shift (also known as parallax) of matched objects to identify depth of these objects.<ref name="kinsman"/> The depth level of each point in the combined image can be represented by a grayscale pixel on a 2D image, for the benefit of the reader. The closer a point appears to the brain, the brighter it is painted. Thus, the way the brain [[Depth perception|perceives depth]] using [[binocular vision]] can be captured by a depth map (Cyclopean image) painted based on coordinate shift.
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[[Image:Stereogram Tut Eye Focus.png|thumb|left|150px|The eye adjusts its internal lens to get a clear, focused image]]
[[Image:Stereogram Tut Eye Convergence.png|thumb|right|150px|The two eyes converge to point to the same object]]
The eye operates like a photographic camera. It has an adjustable [[iris (anatomy)|iris]] which can open (or close) to allow more (or less) light to enter the eye. As with any camera except [[pinhole camera]]s, it needs to [[Accommodation (eye)|focus]] light rays entering through the iris (aperture in a camera) so that they focus on a single point on the retina in order to produce a sharp image. The eye achieves this goal by adjusting a lens behind the cornea to refract light appropriately.

<div id="wall-eyed-viewing">When a person stares at an object, the two eyeballs rotate sideways to point to the object, so that the object appears at the center of the image formed on each eye's retina. In order to look at a nearby object, the two eyeballs rotate towards each other so that their eyesight can [[convergence (eye)|converge]] on the object. This is referred to as ''cross-eyed viewing''. To see a faraway object, the two eyeballs ''diverge'' to become almost parallel to each other. This is known as ''wall-eyed viewing'', where the convergence angle is much smaller than that in cross-eyed viewing.{{efn|name=strabismus|The terms "cross-eyed" and "wall-eyed" are borrowed from synonyms for various forms of [[strabismus]], a condition where eyes do not point in the same direction when looking at an object. Wall-eyed viewing is informally known as parallel-viewing.}}</div>

Stereo-vision based on parallax allows the brain to calculate depths of objects relative to the point of convergence. It is the convergence angle that gives the brain the absolute reference depth value for the point of convergence from which absolute depths of all other objects can be inferred.
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