"SIRDS" is short for "Single Image Random Dot Stereogram". Why the 'Single'? The first random dot stereograms were divided for two pictures, one for each eye. The novel idea to use one instead of two separate images, gave birth to this name. Other widely used nicknames for SIRDS are: RDS, autostereograms, dotty-grams.
"The Stripe" is the vertical part of any SIRDS that is repeated along the vertical axis of the image. The Stripe is actually the building block of the SIRDS.
"echo" we call a 3D object that appear in a SIRDS where it shouldn't. These echos are exact replicas of the 3D objects beside them only a stripe away. The reason they appear is that the way the pattern is coppied makes certain points of the image to have two or more optional heights. An echo usually disappears when one looks at background depth. Most times it is its intended height. Echos are more probable as the eye distance+eye range reduce in width, and at the same time there is a big change in heights horisontally.
"a ghost" is a faint image that is visible at the sides of a 'multiplied' image when viewed in parallel or crossed eyes mothod. for example: if one looks parallely at an image, it becomes two identical ghosts. If one should look and merge two identical images that lie horizontally in fron of him, he should see one solid image and a ghost on each side of it.
Due to way a SIRDS is constructed, the resulting 3D object is not smooth along its depth axis, and looks like a buch of layers or terraces one on top of the other. Good SIRDS use different techniques to increase the number of layers thus makin the 3D world appear a lot smoother.
"Gaps" are holes made in the texture of the resulting SIRDS that evolved from big changes in height of the 3D object. Though gaps do not make it harder to identify the 3D objects in the scene, they are considered unaesthetic.
transparent texture
"Transparent texture" is actually our way to call any texture with an image in the center and a uni-colored border around it.
parallel eyes
"Parallel eyes" is the SIRDS viewing method in which one focuses his vision away behind the image plane in order to see the hidden 3d image.
This is the most common and easy way to look at SIRDS. Most of the stereograms are created for parallel viewing because most people find it easier than using the crossed eye method.
For more on parallel viewing look at Rachel Cooper's Vision3D page.
crossed eyes
"Crossed eyes" is the SIRDS viewing method in which one focuses his vision close in front of the image plane in order to see the hidden 3D image.
many people find it difficult to view crossed eyes images, because one has to strain his eyes to focus on close objects.
For more on crossed eyes viewing look at Rachel Cooper's Vision3D page.