Positional deviation correction using different correction values for monochrome and color bi-directional printing

A bi-directional printing apparatus that bi-directionally prints images on a print medium during forward and reverse main scanning passes, the printing apparatus comprising:

• a print head having a group of nozzles for printing dots on the print medium by emitting ink droplets;
• a main scanning drive mechanism that effects bi-directional main scanning by moving at least one selected from the print medium and the print head;
• a sub-scanning drive mechanism that effects sub-scanning by moving at least one selected from the print medium and the print head;
• a head driver that supplies drive signals to the print head to effect printing on the print medium;
• and
• a controller for controlling bi-directional printing;
• wherein the print head includes:
• an achromatic-color nozzle group that emits ink droplets of an achromatic color;
• and
• chromatic-color nozzle groups comprising a plurality of single chromatic-color nozzle groups each emitting ink droplets of one of a plurality of chromatic colors;
• where in the controller includes a printing position adjuster that uses an adjustment value to reduce printing positional deviation arising between forward and reverse main scanning passes;
• the printing position adjuster having a monochrome printing mode in which a first correction value is used as the adjustment value, and a color printing mode in which a second correction value that is determined separately from the first correction value is used as the adjustment value, the monochrome printing mode using only achromatic color ink, the color printing mode using the achromatic color ink and chromatic color inks.