An image processing method comprising: a first density measurement image formation step (S44) of forming a first image for density measurement on a recording medium in a single-pass method, using an inkjet head in which nozzles are disposed in a main scanning direction (x), based on image data on which unevenness correction processing (S43) using a preset unevenness correction value and defect correction processing (S42) to use a correction nozzle adjacent to a defective nozzle have been performed; a first pre-dry density measurement value acquisition step (S46) of acquiring a first pre-dry density measurement value of the first image for each set gradation value and each of the nozzles, before the first image has dried; a density measurement value conversion step (S47) of converting each first pre-dry density measurement value into a conversion density measurement value corresponding to a post-dry density measurement value, using a first conversion value for each of the nozzles that corresponds to the correction nozzle and a second conversion value for each of the nozzles that does not correspond to the correction nozzle, wherein each of the first conversion value and the second conversion value has been pre-saved and shows a conversion relationship of the first pre-dry density measurement value to the conversion density measurement value for each set gradation value and each of the nozzles; an unevenness correction value derivation step (S48) of deriving a new unevenness correction value for each set gradation value and each of the nozzles using the respective conversion density measurement value; and an unevenness correction processing step (S63) of performing an unevenness correction processing on another image data using the new unevenness correction value. a first density measurement image formation step (S44) of forming a first image for density measurement on a recording medium in a single-pass method, using an inkjet head in which nozzles are disposed in a main scanning direction (x), based on image data on which unevenness correction processing (S43) using a preset unevenness correction value and defect correction processing (S42) to use a correction nozzle adjacent to a defective nozzle have been performed; a first pre-dry density measurement value acquisition step (S46) of acquiring a first pre-dry density measurement value of the first image for each set gradation value and each of the nozzles, before the first image has dried; a density measurement value conversion step (S47) of converting each first pre-dry density measurement value into a conversion density measurement value corresponding to a post-dry density measurement value, using a first conversion value for each of the nozzles that corresponds to the correction nozzle and a second conversion value for each of the nozzles that does not correspond to the correction nozzle, wherein each of the first conversion value and the second conversion value has been pre-saved and shows a conversion relationship of the first pre-dry density measurement value to the conversion density measurement value for each set gradation value and each of the nozzles; an unevenness correction value derivation step (S48) of deriving a new unevenness correction value for each set gradation value and each of the nozzles using the respective conversion density measurement value; and an unevenness correction processing step (S63) of performing an unevenness correction processing on another image data using the new unevenness correction value. <EOS>