par·al·lax (p r  -lks )n. The apparent displacement of an object caused by a change in the position from which it is viewed. par al·lactic (-lkt k) adj. |
parallax
[per′əlaks]
Etymology: Gk, parallelos, side-by-side
the apparent displacement of an object at different distances from the eyes when viewed by both eyes together. It is the basis of stereoscopic vision and depth perception.
parallax (per´
laks),n the apparent change in position of an object when viewed from two different positions. The phenomenon is useful in determining the relative position of an object in a radiograph. Two or more radiographs are made from slightly different positions and the direction and amount of shift of the object is observed and measured.
parallax
Apparent displacement of an object viewed from two different points not on a straight line with the object.
binocular parallax The difference in angle subtended at each eye by an object that is viewed first with one eye and then with the other.
chromatic parallax Apparent lateral displacement of two monochromatic sources (e.g. a blue object and a red object) when observed through a disc with a pinhole placed near the edge of the pupil. When the pupil is centred on the achromatic axis (in some people the pinhole may have to be placed away from the centre of the pupil), the two images appear superimposed. The relative displacement of the two images becomes reversed when the pinhole is on the other side of that axis. This phenomenon is attributed to the chromatic aberration of the eye. See chromostereopsis; longitudinal chromatic aberration.
monocular parallax The apparent change in the relative position of an object when the eye is moved from one position to another.
motion parallax Apparent difference in the direction of movement or speed produced when the subject moves relative to his environment (Fig. P2). Example: when viewing the landscape through the window of a moving train near objects appear to move much more quickly than distant objects. See depth perception; stereopsis.
relative binocular parallax See stereoscopic visual acuity.
binocular parallax The difference in angle subtended at each eye by an object that is viewed first with one eye and then with the other.
chromatic parallax Apparent lateral displacement of two monochromatic sources (e.g. a blue object and a red object) when observed through a disc with a pinhole placed near the edge of the pupil. When the pupil is centred on the achromatic axis (in some people the pinhole may have to be placed away from the centre of the pupil), the two images appear superimposed. The relative displacement of the two images becomes reversed when the pinhole is on the other side of that axis. This phenomenon is attributed to the chromatic aberration of the eye. See chromostereopsis; longitudinal chromatic aberration.
monocular parallax The apparent change in the relative position of an object when the eye is moved from one position to another.
motion parallax Apparent difference in the direction of movement or speed produced when the subject moves relative to his environment (Fig. P2). Example: when viewing the landscape through the window of a moving train near objects appear to move much more quickly than distant objects. See depth perception; stereopsis.
relative binocular parallax See stereoscopic visual acuity.
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Fig. P2 An example of motion parallax
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