There are a number of undesirable effects you may experience when viewing stereo photos. Some of them make it difficult or uncomfortable to fuse the images. Others just detract from the viewing experience. Some of these effects include the following:
- Pseudeoscopic effects. As you begin freeviewing you'll see how parallel pairs are arranged so the image for the left eye is on the left and the image for the right eye is on the right. For cross viewing, the images are reversed. If you cross view images arranged for parallel viewing, or parallel view images arranged for cross viewing, you will experience a unique reversal of perspective called a pusedeoscopic effect. Foreground objects appear in the background and vice-versa.
A commercial stereoview of Glacier Rock, labelled "Transposed prints giving pseudoscopic effect. Copyright 1901 by Underwood & Underwood." The left and right images have been reversed so when you fuse them you'll see how the foreground and background get confused.
- Ghosting, or more technically cross talk, occurs when one eye sees a part of an image meant for the other eye causing a faint double image to appear. This unwanted effect is more common in some technologies, such as anaglyphs, than in others.
- Alignment problems occur when the images are vertically misaligned or rotated. This problem is more common when you take the two images in a stereo pair separately. However, even images taken with a twin lens camera may require adjustment in their vertical alignment.
- Stereo window violations occur when the stereo window is not set correctly so objects in the scene seem to be extending through the window into your viewing space while being cut off by the window behind it. You can adjust the position of this window as discussed in Chapters 3 and 4.
- The puppet theater effect (also known as the Lilliputian effect) occurs when objects in a scene look miniaturized and people appear as small puppets. The effect is more common when we know the size of the portrayed subjects and when the lenses used to take the images are separated by more than the distance between our eyes—called hyperstereo.
- Gigantism occurs when normal sized objects appear gigantic. This can occur when the lenses used to take the images are separated by less than the distance between our eyes—as they would normally be in close-up photography—called hypostereo.
- The cardboard effect is caused when there are few distance cues intervening between major subjects. The scene appears to be cut into a limited number of layers without continuous depth. This effect may appear should the focal lengths of the lenses used to capture and view the images not be identical, or the distance between the lens not be the same.
The images are correct in the left image and reversed in the right. To see pseudeoscopic effects use red/cyan glasses to look carefully at the hole in the rock in both images.
When viewed in color with red/cyan glasses the wing seems to be extending through the stereo window into your space while being cut off by the window behind it—a window violation.
A SINGLE POINT OF VIEW
Once you fuse images you can move your head from side to side to see around objects in the foreground but you'll only see the scene from the point of view of the two lenses at the time the image was taken.