Control device for controlling printer having print head

A non-transitory computer readable storage medium storing a set of program instructions for a control device for controlling a printer, the printer comprising:

• a print head configured to move in a main scanning direction and having a plurality of nozzles arranged in a sub-scanning direction perpendicular to the main scanning direction, each of the plurality of nozzles being configured to eject a droplet of coloring material onto a printing medium, the control device comprising a controller, the set of program instructions, when executed by the controller, causing the control device to perform:
• acquiring target image data representing a target image, the target image including a plurality of unit images, each of the plurality of unit images extending in the main scanning direction;
• specifying a target unit image among the plurality of unit images, the target unit image including N number of partial images arranged in the main scanning direction, where N is an integer equal to or greater than two;
• specifying J number of target partial images among the N number of partial images, where J is an integer equal to or greater than one and equal to or smaller than N;
• calculating J number of index values corresponding to respective ones of the J number of target partial images, each of the J number of index values being calculated using a plurality of pixel values of a plurality of pixels included in corresponding one of J number of target partial data, the J number of target partial data representing respective ones of the J number of target partial images;
• determining whether to print the target unit image according to the J number of index values;
• in response to determining to print the target unit image, controlling the printer to execute ejection processing and movement processing for printing a band image onto the printing medium, the band image constituted with H number of successive unit images arranged in the sub-scanning direction and including the target unit image, the ejection processing ejecting the droplet of the coloring material onto the printing medium while moving the print head in the main scanning direction, the movement processing moving the printing medium in the sub-scanning direction with respect to the print head, where H is an integer equal to or greater than one;
• and
• in response to determining not to print the target unit image, controlling the printer to execute the movement processing but not execute the ejection processing for printing the target unit image onto the printing medium.