Image distortion
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In geometric optics and cathode ray tube (CRT) displays, image distortion is a deviation from rectilinear projection, a projection in which straight lines in a scene remain straight in an image.
Although distortion can be irregular or follow many patterns, the most commonly encountered distortions are radially symmetric, or approximately so, arising from the symmetry of a photographic lens. The radial distortion can usually be classified as one of two main types:
- barrel distortion, in which image magnification decreases with increasing distance from the optical axis. The apparent effect is that of an image which has been mapped around a sphere. Fisheye lenses, which take hemispherical views, produce this type of distortion as a result of a hemispherical scene being projected onto a flat surface.
- pincushion distortion, in which image magnification increases with increasing distance from the optical axis. The visible effect is that lines that do not go through the centre of the image are bowed inwards, towards the centre of the image. In photography, this aberration is often seen in older or low-end telephoto lenses.
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