From horizontal and vertical coordinate values HC and VC of a pixel, a distance operation unit calculates a distance value RV indicating the distance from an optical-axis position to the pixel. A correction-data operation unit receives the distance value RV, and calculates correction data CD for the pixel by referring to an approximation function indicating relation between distance values and correction data. The approximation function is divided into a plurality of segments, and in each segment represented by a quadratic function defined by a predetermined number of sample points.