Wide-eyed Wonder: an artist's musings on three-dimensional vision

Some are color blind. I am stereo blind.

– Vision depth cues we all use

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Folks with normal vision and those with stereo blindness both use Monocular or Extrastereoscopic Cues to get around in life. 3dathome.org defines these as:

Those depth cues appreciat­ed by a person using only one eye. Also called monoc­ular cues. They include interposition, geometric perspective, motion parallax, aerial perspective, relative size, shading, and textural gradient.

Let’s dig deeper into each vision depth cue

Overlapping objects indicate depth

Interposition, Overlap,
Overlay or Occlusion

… is the partial blocking of a more distant object by a nearer object.[1]
Relative Size
The more distant an object … the smaller the image of that object will be on your retina, the back of the eye … An object’s smaller size on your retina when it is farther away from you is called relative size.[2]
Closely related to relative size is textural gradient, the relative size of details and textures on the things one is viewing.
“… a depth cue in its own right is what has been termed texture gradient. Most surfaces, such as walls and roads and a field of flowers in bloom, have a texture. As the surface gets farther away from us this texture gets finer and appears smoother.” Gibson, J. J. (1950). The perception of the visual world. New York: Houghton Mifflin

Linear Perspective

Geometric or Linear Perspective
Geometric perspective is a drawing method by which it is possible to depict a three-dimensional form as a two-dimensional image that closely resembles the scene as visualized by the human eye. The camera produces photographs with such resemblance.[3]

In the case of the stereo blind, geometric perspective is a natural monocular cue heavily used not just for drawing, but to visualize and understand depth in real life.

Motion Parallax
The perception of objects moving at different speeds relative to their distance from the observer.[4]

Animals also use motion parallax, in which the animals (or just the head) move to gain different viewpoints. For example, pigeons (whose eyes do not have overlapping fields of view and thus cannot use stereopsis) bob their heads up and down to see depth.[5]

Aerial Perspective
The blueing and slight blurring (of distant objects affected by the atmosphere) is called aerial perspective. These techniques have been used in painting and do help give the impression of depth.[6]
Last, but not least, what makes objects appear most 3D for me is the way the light hits a thing and creates “3 dimensional shape” with shading and shadows.
There are 5 key components of light and shadow: the highlight, core shadow, midtone shadow, cast shadow and bounced or reflected light into a core shadow.

Written by Lynda Rimke

January 20, 2011 at 10:10 pm

One Response

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  1. […] and pop culture examples she offers her notes on Frederick Brock’s work and examples of visual cues that convey depth, the only way we strabbies see 3D.  I admire Josh’s ingenious vision therapy inventions and […]

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