An image processing apparatus regardless of usage environment, at any time, for any occasion, without requiring a dedicated chart or device, spatial frequency conversion method and program for the apparatus that can calculate spatial frequency response characteristics necessary for calibration. The apparatus includes first and second image reading units reading a print-out image of a patch image stored in a storage section, and first and second spatial frequency conversion units performing spatial frequency conversion on images read by first and second reading units. Based on the amounts of change, caused through processing by first spatial frequency conversion unit, in spatial frequency response, the apparatus determines a patch image used for spatial frequency conversion, and calculates correction amounts for conversion by first and second spatial frequency conversion units, according to a result of spatial frequency conversion, using the patch image, by first and second spatial frequency conversion units.