In optics, distortion refers to the deviation of an image from the ideal shape or proportions of the object that is being photographed or viewed through a lens system. Unlike other optical aberrations, such as spherical aberration or chromatic aberration, distortion specifically affects the geometry of the image rather than its sharpness or color fidelity.
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Optical distortion is a position-dependent change of image scale: a system fails to map object coordinates by one uniform magnification. It can bend the images of straight lines even when individual image points remain sharp.
Photographing a rectangular grid makes the effect concrete. When the radial image scale decreases toward the edge, the grid bows outward in the familiar barrel pattern; the opposite tendency produces a pincushion pattern. A calibrated coordinate mapping can correct geometry in a recorded image, but cannot recover detail already lost through blur, coarse sampling or clipping.