A non-transitory recording medium storing a program that, when executed by a computer, causes the computer to execute a method, the method comprising:
- moving a print head unit in a scanning direction perpendicular to a sub-scanning direction with respect to a print medium, while causing discharge of liquid onto the print medium, the print head unit including a nozzle array with a plurality of nozzles in a sub-scanning direction, each nozzle being configured to discharge liquid onto the print medium, and the print head unit being either a head array with a plurality of heads or any one of the plurality of heads;
- moving, without causing discharge of the liquid, the print medium or the print head unit in the sub-scanning direction, moving of the print head unit in the scanning direction and moving of the print medium or the print head unit in the sub-scanning direction being, alternately performed;
- setting a line pitch by which the print head unit moves, per scan with respect to the sub-scanning direction;
- performing a gradation mask operation in which, in the sub-scanning direction, the number of dots of liquid discharged from the nozzles is decreased toward both end portions, as gradation areas, of a gradation mask formed through the print head unit, the both end portions of the gradation mask corresponding to both end portions of the print head unit;
- causing the nozzles of the print head unit to discharge liquid based on image data;
- selecting, as the print head unit that is assigned to the gradation mask, either the head array or the one head, based on image density derived from the image data;
- and
- detecting a gloss of an image that is formed on the print medium by assigning the selected print head unit to the gradation mask and to enable feedback control in the gradation mask operation, based on a detected result,
- wherein the gradation mask operation is performed using a combination of four gradation curve functions and a random function for randomly arranged dots, the four gradation curve functions being a first gradation curve function, a second gradation curve function, a third gradation curve function, and a fourth gradation curve function,
- wherein a first combination of a first gradation curve marked through the first gradation curve function and a second gradation curve marked through the second curve function is marked in a first end portion of the gradation mask, among the both end portions, and a second, combination of a third gradation curve marked through the third gradation curve function and a fourth gradation curve marked through the fourth gradation curve function is marked in a second end portion of the gradation mask,
- wherein the first gradation curve and the second gradation curve are point-symmetric about a point that is a midpoint of the first end portion of the gradation, mask, and wherein the third gradation curve and the fourth gradation curve are point-symmetric about a point that is a midpoint of the second end portion of the gradation mask,
- wherein, in the sub-scanning direction, a combination of the first gradation curve and the third gradation curve are line-symmetric with respect to a point that is a midpoint of the plurality of nozzles of the nozzle array in the print head unit, and wherein, in the sib scanning direction, a combination of the second gradation curve and the fourth gradation curve are line-symmetric with respect to a point that is a midpoint of the plurality of nozzles of the nozzle array in the print head unit,
- wherein, in the sub-scanning direction, each gradation area of the gradation mask has a width of an integer multiple of the line pitch, and
- wherein the causing discharge of liquid onto the print medium includes causing the print head to discharge the liquid onto the print medium, at an offset by the line pitch, such that same gradation areas of the gradation mask partially overlap with respect to continuous forward scanning and backward scanning in the scanning direction.