In addition to the depth cues I talked about in the previous post, all of which can be exploited in pictures, there are 4 cues which are very powerful, particularly in judging the distance of things close by, in personal space.
Unfortunately these cues arise only in the presence of motion or stereoscopic vision, and can't be reprodiuced in drawings! They're mentioned here for interest only.
1. binocular disparities
– The left
and right eyes see a slightly different angle of an object. If an object is far
away, the disparity of that image falling on both retinas will be small, and
the effect is not noticeable. If the object is near, in personal space, the
disparity will be large. Hold a finger up at arm’s length and close each eye
alternately – notice how you have a different field of view in each eye.
2. motion parallax
- When an
observer moves, the apparent relative motion of several stationary objects
against a background gives hints about their relative distance. This is very noticeable
when watching the landscape from a moving train.
3. convergence
- When the two eye
balls focus on the same object they are said to converge. This convergence stretches
the muscles attached to the eyeball. The angle of convergence, and hence the
muscle stretch, is smaller when the eye is
fixating on far away objects, and hence is not very effective at a distance of
over 10 metres. It becomes most effective at very close range, particularly
within personal space.
4. accommodation
- This is another
muscular cue for depth perception. When we try to focus on far away objects,
the muscles of the lens in the eye stretch, making the lens thinner, to change the focal length. The sensation
of these muscles contracting and relaxing is used by the brain for interpreting
distance/depth. Like other muscular cues accommodation is only effective close
up, within personal space.
No comments:
Post a Comment