Stereoscopy

Why Stereoscopy Can Cause Pain

2009-09-05T18:54:00.000-07:00

There is one major difference in how we naturally see objects and how we view them on stereoscopic images. When viewing objects in the natural world we pull focus and converge our eyes onto an object. This does not occur in stereoscopy as the viewer's eyes are focused on the viewing plane (computer screen) at all times.

Warning!! Because we are force-fed image data that does not occur in the natural world this can cause a physical pain response to a mental incomprehension especially so when the force-fed image data has an excess of parallax.

as a rule of thumb use 1.5 degrees or approximately only 1.5 in or 12 mm as a maximum distance for generated images with parallax for a viewing distance of 1.5 feet. As your distance becomes greater the maximum distance of parallax also is granted.

always try to use the least amount of parallax in order to achieve the desired effect to minimize problems.

Interaxial Seperation

2009-09-05T18:43:00.000-07:00

Interaxial Seperation is specific to the distance between two cameras in a stereoscopic rig for taking stereoscopic images in the real or virtual world.

for our purposes we must use cameras that are perpendicular to each other or problems of parallax for the viewer will occur causing things that do not happen naturally to potentially occur and pain.

keep your cameras parallel!

Binocular vision

2009-09-05T18:22:00.000-07:00

because of our two eyes a couple interesting factors occur when we come to perceive sight.

Retinal Disparity occurs due to our separated eyes that are focusing on an object.

when an object in focus is a single solid image this object is said to have zero disparity the process in which this occurs is called fusion.

Parallax:
This is where things get tricky. There are four basic kinds of parallax for stereoscopic uses

ZPS or Zero Parallax setting occurs when your eyes converge onto a surface. This occurs every time you look at your computer screen. Our goal in stereoscopy is to give three dimensional cues to a viewer feeding them images with parallax which does not occur normally on a two dimensional medium.

Positive parallax occurs when seeing objects naturally at a great distance. the distance between the focus of your eyes become almost parallel. in relation to a computer screen objects with positive parallax appear to be on or behind the computer screen.

Divergent Parallax is the divergence of the eyes. It does not occur in natural vision and causes great discomfort so it is not utilized in stereoscopy.

Negative Parallax is in essence the act of crossing your eyes. Objects in Negative Parallax appear to be closer to the viewer than the computer screen.

Monocular Cues

2009-09-05T17:35:00.000-07:00

In precieving three dimentional space the brain deciphers a multitude of factors which helps discern what is further and what is closer

Some of these cues do not need two eyes in which to aid 3D detection, these are called Monocular Cues

some Monocular cues include:

Light and Shade alone is able to make objects appear three dimensional as they lay on top of each other as overlapping three dimensional objects in the real world are affected by a light source giving cues to shape and form. With hard and soft shadows we can discern how an object sits on a surface.

Relative Size goes hand in hand with perspective. Because of our knowledge things look smaller as they are farther away we are able to utilize this depth cue

Interposition is the fact that objects can overlap. When things overlap the object on top will always have more visibility than what is below it if any at all.

as objects come closer more Texture detail is apparent in it's material

as objects reach far distances Atmospheric Haze/Perspective takes effect. Atmospheric Haze and atmospheric perspective is caused by dust particles in the air that cause objects to fade in the distance

Motion Paralax is exclusively a motion cue. Things in the distance will appear to move much slower than things closer to you.

Perspective is one of the strongest depth cues. It is in essence a combination of most of the other depth cues. By emphasizing a vanishing point a strong three dimensional effect can be achieved

Depth of Field is a strong indicator of the detection of images in three dimensions allowing us to pull focus on a certain object, however achieving this effect is difficult in stereoscopy