A distance calculation method and an imaging device that can be applied to
a digital camera. The method includes calculating a distance between a
point corresponding to an optical axis of a lens sub-system of the
imaging device and an input point, and using the calculated distance to
correct defects such as shading that occur in formed images due to
peripheral light fall-off in the lens sub-system. The distance is
approximated by a polygon having five or more sides, preferably having 8
or 16 sides. The distance is calculated by a disclosed function having
constant coefficients, so that distances can be calculated by simple
hardware.