Image processor and image processing method having correcting unit performing correction based on correction parameters

An image processor which processes input image data for printing an image on a plurality of regions of a print medium with the use of print heads provided with a plurality of nozzle arrays including a first nozzle array and a second nozzle array, the first nozzle array including first nozzles for ejecting first ink arranged in a predetermined direction and the second nozzle array including second nozzles for ejecting second ink, having a different color from the first ink, arranged in the predetermined direction, the image processor comprising:

• a correcting unit configured to correct the input image data on the basis of a plurality of existing correction parameters, each of which corresponding to one of a plurality of nozzle groups and one of the plurality of regions, for converting the input data including a plurality of components into corrected image data including a plurality of components, for reducing color deviation of an image represented by the first ink and the second ink, and wherein each of the plurality of nozzle groups includes one of the first nozzles and one of the second nozzles which are capable of ejecting ink for the same region of the plurality of regions;
• an acquiring unit configured to acquire, for each of the plurality of nozzle groups, a first ejection characteristic of the first nozzle and a second ejection characteristic of the second nozzle;
• and
• a determining unit configured to determine, for each of the plurality of regions, a necessity to generate a new correction parameter as a correction parameter which is used by the correcting unit to replace at least one of the existing correction parameters on the basis of both the first ejection characteristic and the second ejection characteristic acquired by the acquiring unit,
• wherein the first ejection characteristic indicates a first difference between a value indicating the ejection amount of the first ink acquired by the acquiring unit and a value indicating the previous ejection amount of the first ink that had been acquired when the existing correction parameters were generated,
• and wherein the second characteristic indicates a second difference between a value indicating the ejection amount of the second ink acquired by the acquiring unit and a value indicating the previous ejection amount of the second ink that had been acquired when the existing correction parameters were generated.