Patent ID: 8451334

Claim:
A calibration pattern for an imaging device, the calibration pattern configured to be captured by an imaging device to correct measurement error of the imaging device that measures a length of an object based on a captured image of the object, the calibration pattern comprising: a central portion provided with one of a rectangular light area and a rectangular dark area in a central portion of the calibration pattern and; a frame pattern provided outside the central portion and comprising a plurality of rectangular frame-shaped portions, each rectangular frame-shaped portion of the plurality of rectangular frame-shaped portions comprising a pair of horizontal sides and a pair of vertical sides, wherein: the plurality of rectangular frame-shaped portions comprises a plurality of light area frame-shaped portions and a plurality of dark area frame-shaped portions, each light area frame-shaped portion of the plurality of light area frame-shaped portions and each dark area frame-shaped portion of the plurality of dark area frame-shaped portions is alternately provided outwardly from and about the central portion at a predetermined interval different from an equal interval, the frame patterns each comprise edges, each edge being a boundary between a said light area frame-shaped portion and a said dark area frame-shaped portion at a position equally distant from a predetermined position in the central portion to the pair of vertical and horizontal sides, and the edges have an identical change direction of a gray value, the gray value defined as a value between a respective said light area frame-shaped portion and a respective said dark area frame-shaped portion.