1. An image processing apparatus that processes image data of multiple pixels constituting an image, said image processing apparatus comprising: a dot on-off setting module that determines dot on-off state in each pixel of the image to create dots at a preset density corresponding to a tone value of the image data in such a manner that a distribution of dots is to be weighted in a specific direction, which is different from a direction of raster lines aligned as arrays of dots; and a data supply module that supplies data representing positions of dots to be created as control data for dot formation to a printing module that actually creates dots.