Correction processing on image data is performed in a short time. An image processing apparatus supplies image data to a recording apparatus configured to convey a recording medium in a direction intersecting a direction in which recording elements are arranged. The image processing apparatus includes: tables containing correction information for each group into which the recording elements are divided, the correction information being used to correct values of multi-valued data; a horizontal/vertical conversion unit configured to convert multi-valued data in raster format into column format; a correction unit configured to correct multi-valued data belonging to a group by using correction information stored in a table corresponding to that group; a vertical/horizontal conversion unit configured to convert the multi-valued data in column form into raster format; and an output unit configured to output the data in raster format converted by the vertical/horizontal conversion unit to the recording apparatus.