Shading correction method and apparatus

摘要

Shading correction is effected by partitioning a white standard surface into a plurality of scanning blocks having the same number of scanning lines, scanning the standard surface by block to determine block median values in a first processing stage, determining global median values from the block median values in a second processing stage, and subjecting objective image data read from a given original image to arithmetic such as proportioning calculation. With the two-stage processing, shading distortion caused due to nonuniformity in sensitivity of an image scanning system can be rationally and reliably corrected to a high degree with a simple processing circuit.