Editing Autostereogram (section)

===Viewing techniques===
[[File:Mariposas autoestereoscópicas.JPG|thumb|Butterflies, cross-eyed autostereogram ([[File:Stereogram guide cross-eyed.svg|10px]])]]

If one has two eyes, fairly healthy eyesight, and no neurological conditions which prevent the perception of depth, then one is capable of learning to see the images within autostereograms. "Like learning to ride a bicycle or to swim, some pick it up immediately, while others have a harder time."<ref>Kosslyn and Osherson (1995), p. 64.</ref>

As with a [[Camera|photographic camera]], it is easier to make the eye focus on an object when there is intense ambient light. With intense lighting, the eye can constrict the [[pupil]], yet allow enough light to reach the retina. The more the eye resembles a [[pinhole camera]], the less it depends on [[Accommodation (vertebrate eye)|focusing]] through the [[lens (vertebrate anatomy)|lens]].{{efn|See [[aperture]] on similarity between aperture and pupil. See [[depth of field]] for relationship between aperture and lens.}} In other words, the degree of decoupling between focusing and convergence needed to visualize an autostereogram is reduced. This places less strain on the brain. Therefore, it may be easier for first-time autostereogram viewers to "see" their first 3D images if they attempt this feat with bright lighting.

[[Vergence]]<!--"vergence" is a real word spelled correctly--> control is important in being able to see 3D images. Thus it may help to concentrate on converging/diverging the two eyes to shift images that reach the two eyes, instead of trying to see a clear, focused image. Although the [[accommodation reflex|lens adjusts reflexively]] in order to produce clear, focused images, voluntary control over this process is possible.<ref>{{cite journal |first1=Leon N. Jr |last1=McLin |first2=Clifton M. |last2=Schor |title=Voluntary effort as a stimulus to accommodation and vergence |journal=Investigative Ophthalmology & Visual Science |date=1988 |volume=29 |number=11 |pages=1739–1746 |pmid=3182206}}</ref> The viewer alternates instead between converging and diverging the two eyes, in the process seeing "double images" typically seen when one is [[drunkenness|drunk]] or otherwise intoxicated. Eventually the brain will successfully match a pair of patterns reported by the two eyes and lock onto this particular degree of convergence. The brain will also adjust eye lenses to get a clear image of the matched pair. Once this is done, the images around the matched patterns quickly become clear as the brain matches additional patterns using roughly the same degree of convergence.

[[Image:Chess Single Image Stereogram by 3Dimka.jpg|thumb|400px|A type of wallpaper autostereogram featuring 3D objects instead of flat patterns ([[Image:Stereogram guide parallel.png|10px]])]]
[[Image:Stereogram Tut Shark Bottom Clear.png|thumb|400px|The bottom part of this autostereogram is free of 3D images. It is easier to trick the brain into matching pairs of patterns in this area. ([[Image:Stereogram guide parallel.png|10px]])]]
When one moves one's attention from one depth plane to another (for instance, from the top row of the chessboard to the bottom row), the two eyes need to adjust their convergence to match the new repeating interval of patterns. If the level of change in convergence is too high during this shift, sometimes the brain can lose the hard-earned decoupling between focusing and convergence. For a first-time viewer, therefore, it may be easier to see the autostereogram, if the two eyes rehearse the convergence exercise on an autostereogram where the depth of patterns across a particular row remains constant.

In a random dot autostereogram, the 3D image is usually shown in the middle of the autostereogram against a background depth plane (see the shark autostereogram). It may help to establish proper convergence first by staring at either the top or the bottom of the autostereogram, where patterns are usually repeated at a constant interval. Once the brain locks onto the background depth plane, it has a reference convergence degree from which it can then match patterns at different depth levels in the middle of the image.

The majority of autostereograms, including those in this article, are designed for divergent (wall-eyed) viewing. One way to help the brain concentrate on divergence instead of focusing is to hold the picture in front of the face, with the nose touching the picture. With the picture so close to their eyes, most people cannot focus on the picture. The brain may give up trying to move eye muscles in order to get a clear picture. If one slowly pulls back the picture away from the face, while refraining from focusing or rotating eyes, at some point the brain will lock onto a pair of patterns when the distance between them matches the current convergence degree of the two eyeballs.<ref name="beyond3d"/>

Another way is to stare at an object behind the picture in an attempt to establish proper divergence, while keeping part of the eyesight fixed on the picture to convince the brain to focus on the picture. A modified method has the viewer focus on their reflection on a reflective surface of the picture, which the brain perceives as being located twice as far away as the picture itself. This may help persuade the brain to adopt the required divergence while focusing on the nearby picture.
[[File:Sphere Cube Triangle 3D Stereogram Illusion.png|alt=Sphere Cube Triangle 3D Stereogram Illusion|thumb|400x400px|Mapped Textured Stereogram (MTS) where a textural image is mapped onto a depth-map rather than mapping a random pattern.]]
Those who wear eyeglasses with so-called "progressive" lenses, in which the focal length gradually changes so as to ease the viewing of close objects using the lower part of the lens, may find that viewing a stereogram is easier if the glasses are pushed up a little so that the stereogram is viewed through a part of the lens optimized for images that are closer than the actual distance to the stereogram.  When the eyes are made divergent by looking (or pretending to look) at a far-away object, the overcorrection from viewing the stereogram through the "wrong" part of the lens can bring the stereogram into focus without needing to overcome the tendency to focus on the far-away object while attempting to focus on the stereogram. 

For crossed-eyed autostereograms, a different approach needs to be taken. The viewer may hold one finger between their eyes and move it slowly towards the picture, maintaining focus on the finger at all times, until they are correctly focused on the spot that will allow them to view the illusion.

[[Stereoblindness]], however, is not known to permit the usages of any of these techniques, especially for persons in whom it may be, or is, permanent.