Stereoscopy
Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision.[2] The word stereoscopy derives from Greek στερεός (stereos) 'firm, solid', and σκοπέω (skopeō) 'to look, to see'.[3][4] Any stereoscopic image is called a stereogram. Originally, stereogram referred to a pair of stereo images which could be viewed using a stereoscope.
Several terms redirect here. For other uses, see autostereogram, phonogram, and stereographic projection.
Most stereoscopic methods present a pair of two-dimensional images to the viewer. The left image is presented to the left eye and the right image is presented to the right eye. When viewed, the human brain perceives the images as a single 3D view, giving the viewer the perception of 3D depth. However, the 3D effect lacks proper focal depth, which gives rise to the Vergence-Accommodation Conflict.
Stereoscopy is distinguished from other types of 3D displays that display an image in three full dimensions, allowing the observer to increase information about the 3-dimensional objects being displayed by head and eye movements.
Stereo window[edit]
The concept of the stereo window is always important, since the window is the stereoscopic image of the external boundaries of left and right views constituting the stereoscopic image. If any object, which is cut off by lateral sides of the window, is placed in front of it, an effect results that is unnatural and is undesirable, this is called a "window violation". This can best be understood by returning to the analogy of an actual physical window. Therefore, there is a contradiction between two different depth cues: some elements of the image are hidden by the window, so that the window appears as closer than these elements, and the same elements of the image appear as closer than the window. So that the stereo window must always be adjusted to avoid window violations.
Some objects can be seen in front of the window, as far as they do not reach the lateral sides of the window. But these objects can not be seen as too close, since there is always a limit of the parallax range for comfortable viewing.
If a scene is viewed through a window the entire scene would normally be behind the window, if the scene is distant, it would be some distance behind the window, if it is nearby, it would appear to be just beyond the window. An object smaller than the window itself could even go through the window and appear partially or completely in front of it. The same applies to a part of a larger object that is smaller than the window. The goal of setting the stereo window is to duplicate this effect.
Therefore, the location of the window versus the whole of the image must be adjusted so that most of the image is seen beyond the window. In the case of viewing on a 3D TV set, it is easier to place the window in front of the image, and to let the window in the plane of the screen.
On the contrary, in the case of projection on a much larger screen, it is much better to set the window in front of the screen (it is called "floating window"), for instance so that it is viewed about two meters away by the viewers sit in the first row. Therefore, these people will normally see the background of the image at the infinite. Of course the viewers seated beyond will see the window more remote, but if the image is made in normal conditions, so that the first row viewers see this background at the infinite, the other viewers, seated behind, will also see this background at the infinite, since the parallax of this background is equal to the average human interocular.
The entire scene, including the window, can be moved backwards or forwards in depth, by horizontally sliding the left and right eye views relative to each other. Moving either or both images away from the center will bring the whole scene away from the viewer, whereas moving either or both images toward the center will move the whole scene toward the viewer. This is possible, for instance, if two projectors are used for this projection.
In stereo photography window adjustments is accomplished by shifting/cropping the images, in other forms of stereoscopy such as drawings and computer generated images the window is built into the design of the images as they are generated.
The images can be cropped creatively to create a stereo window that is not necessarily rectangular or lying on a flat plane perpendicular to the viewer's line of sight. The edges of the stereo frame can be straight or curved and, when viewed in 3D, can flow toward or away from the viewer and through the scene. These designed stereo frames can help emphasize certain elements in the stereo image or can be an artistic component of the stereo image.