Control device and control method for controlling printing unit to perform multi-pass printing

A control device configured to control a printing unit to execute a multi-pass printing, the printing unit including a print head, first conveying unit, a head driving unit, and a second conveying unit, the print head having a plurality of nozzles, the first conveying unit configured to reciprocate the print head in a first direction relative to a printing medium, the head driving unit configured to drive the print head to form ink dot on the printing medium, the second conveying unit configured to convey the printing medium in a second direction perpendicular to the first direction, the control device comprising:

• a multi-pass execution unit configured to control the printing unit to execute the multi-pass printing for a predetermined partial area of the printing medium by executing a main scan and a sub-scan a prescribed number of times, wherein in the main scan, the print head forms the ink dot on the printing medium while being conveyed by the first conveying unit in the first direction, and in the sub-scan, the second conveying unit conveys the printing medium in the second direction;
• an acceptable range determining unit configured to determine an acceptable range of gradation values based on an actual error in a conveyance amount of the second conveying unit;
• and
• a number setting unit configured to set the prescribed number based on the acceptable range of gradation values and a representative gradation value of the predetermined partial area;
• wherein the number setting unit sets the prescribed number to N where N is an integer greater than or equal to 2 when the representative gradation value falls in the acceptable range of gradation values, and the number setting unit sets the prescribed number to M where M is an integer greater than N when the representative gradation value does not fall in the acceptable range of gradation values.