The stereopsis and three-dimensional vision that stems from the simultaneous stimulation of horizontally disparate retinal points by Point object located within the areas of Panum. Stereoscopic acuity and the minimum disparity beyond which you do not have any stereoscopic effect. Values \u200b\u200bof about 15-30 seconds of arc, ie 0.004 ° -0008 °, are considered excellent. Note that the angle of stereoscopic acuity and about 15 times less than the minimum angle of ocular convergence sensitive. This sembrebbe imply that the perception of depth is greater due to stereopsis compared to other phenomena, in particular with regard to convergence eye.
depth perception does not depend then only by binocular vision, but the result of a set of mental processes and perceptual phenomena and physiological knowledge of which makes it possible to artificially recreate the feeling of distance, or, in special cases, to situations and paradoxical.
The visual arts, particularly painting with perspective, photography and cinematography, these processes are often exploited, sometimes by doing calculations on artificial visual material, to get the feel of the desired distance.
In particular, there are many monocular elements, ie observable and effective in one eye, which contribute to the assessment of the relative distance between objects observed, and some of them are:
- Motion parallax: the speed of movement of a nearby object appears to be greater than that of a distance.
- The linear perspective: an object of constant magnitude behind corners progressively smaller (and therefore seen smaller), as it moves away. The most classic example is the apparent convergence of two parallel lines that move away from the viewer. - The overlap of contours: an object that interrupts the contours of another is perceived to be prefixed to another.
- The distribution of light and shadows: the light and shade generates a feeling of relief and then depth.
- Familiarity with known objects: the distance between known objects is also judged according to their apparent size.
- The aerial perspective: atmospheric haze influence the contrast and color of objects located farther. It also blurs the boundaries. The phenomenon is often used in photography focusing on the main subject and artistically blurring the other plans, in particular the background.
binocular elements, ie those that are perceived with both eyes, add detail and quality of the perceived distance. The main element and the binocular convergence optical axes of the eye, as permitted by extrinsic muscles. Moreover, convergence on points at more than 30 meters from the observer (angle of convergence of about 4 ', ie 0062 °) obtained with angular displacements of the eyeball is too small to be felt and measured. Of more interest in stereoscopy and stereopsis, namely the three-dimensional view that originates from the analysis of small differences between the images transposed from both eyes. In reality, in fact, an object occupies a volume not null and is perceived as a set of points covered by projecting its image on as many pairs of retinal points. The object points located close by falling or sull'oroptero or in the Panum and are then merged into single points. However generate retinal disparity in the analysis and measurement by the perceptual system object gives impression of solidity and depth. Stereopsis is therefore the slight disparity with which they are seen as long as items are included in the Panum, that as long as they are precepiti without diplopia.
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