Image forming apparatus, image forming method, and image forming program

An image forming apparatus includes: a nozzle head in which nozzles that ejects ink is arranged in a first direction; a moving mechanism that moves a recording medium relative to the nozzle head; an image acquirer that acquires image data; a quantization processor that quantizes density of pixels forming an image based on the image data; a grouping processor that groups adjacent pixel positions into one group in the quantized data; and a rearrangement processor that rearranges a quantized pixel value at each pixel position in the group that is grouped, wherein the grouping processor groups such that a direction intersecting the first direction is set to a second direction, arrangement of groups in the first direction is set to a row, rows is arranged in the second direction, and a row in which an initial position of the row is different at least by one pixel is included.