Wiggle stereoscopy is to simply alternate between the left and right images of a stereogram. This can easily be accomplished with an animated .gif image, flash applet or a specialized java applet. Most people can get a crude sense of dimensionality from such images, due to persistence of vision and parallax.
Closing one eye and moving the head from side-to-side when viewing a selection of objects helps one understand how this works. Objects that are closer appear to move more than those further away. This effect may also be observed by a passenger in a vehicle or low-flying aircraft, where distant hills or tall buildings appear in three-dimensional relief, a view not seen by a static observer as the distance is beyond the range of effective binocular vision.
Advantages of the wiggle viewing method include:
- No glasses or special hardware required
- Most people can "get" the effect much quicker than cross-eyed and parallel viewing techniques
- It is the only method of stereoscopic visualisation for people with limited or no vision in one eye
Disadvantages of the "wiggle" method:
- Does not provide true binocular stereoscopic depth perception
- Not suitable for print, limited to displays that can "wiggle" between the two images
- Difficult to appreciate details in images that are constantly "wiggling"
Most wiggle images use only two images, leading to an annoyingly jerky image. A smoother image, more akin to a motion picture image where the camera is moved back and forth, can be composed by using several intermediate images (perhaps with synthetic motion blur) and longer image residency at the end images to allow inspection of details. Another option is a shorter time between the frames of a wiggle image through the use of an animated .png.
Although the "wiggle" method is an excellent way of previewing stereoscopic images, it cannot actually be considered a true three-dimensional stereoscopic format. To experience binocular depth perception as made possible with true stereoscopic formats, each eyeball must be presented with a different image at the same time – this is not the case with "wiggling" stereo. The apparent "stereo like effect" comes from syncing the timing of the wiggle and the amount of parallax to the processing done by the visual cortex. Three or five images with good parallax produce a much better effect than simple left and right images. Recent research indicates that binocular vision is the results of timing and phase disparities in the visual cortex. See the references below on binocular disparity as well as timing and phase differences in a process called binocular rivalry. By timing the wiggle just right and using the right amount of parallax we can fool the neural cortex into registering the sensation of binocular vision.