suomeksi (in Finnish)
What is stereoscopy?
Stereoscopic images are image pairs, which are directed to separate eyes by using special viewing techniques or equipment. The result is an illusion of a single actually three-dimensional image. The phenomen is based on the fact, that we see the world always from two slightly different angles simultaneously.
How do you view sterescopic images?
It is possible to see three dimensional stereoscopic images with bare eys. It can be done by parallel viewing or cross-eyed viewing. In parallel viewing the eys are focused behind the actual image surface, so that the left eye sees the left image and the right eye sees the right one. In this case, the distance between the image pair (i.e. the width of the images) should not be longer than the distance between the two eyes (appr. 6.5 cm).
In cross-eyed viewing the eyes are focused between the image surface and the eyes. The left image is seen by the right eye and vice versa. The images can be larger than the distance between the eyes, but larger images are not comfortable to look at.
The below image can be viewed using parallel viewing.
A stereoscopic image pair
By using special equipment the viewing of 3D images can be made easier and the limitation of the small image size can be removed.
Stereograms have been made possible by computer graphics. They are a special form of stereoscopic images where the two images are mixed into a single one so that they can be viewed without any equipment nevertheless. The pictures are formed of repeating vertical bands, and the changes in depth are achieved by altering the horisontal density of the pattern. The eyes are focused behind the surface so that the bands next to each other are merged (as though the bands formed an image pair viewed with the parallel technique). Cross-eyed method can also be used.
The way the stereograms work:
Stereograms can be divided into random stereograms which are made of random pattern vertical bands and wall paper stereograms, which have repeating recognizable forms or small images. Wall paper stereograms are actually series' of several normal stereo image pairs.
This is a random stereogram.
This is a wall paper stereogram.
These two types can also be mixed: