A plurality of nozzles in use are classified into M nozzle groups, each nozzle group including Neff nozzles, where Neff is an integer of not less than 2 and M is an integer of not less than 2. A plurality of dot positions on each raster line are also classified into M different types of dot positions. The Neff nozzles included in each nozzle group execute dot recording at one identical type of dot positions, whereas the different nozzle groups respective execute dot recording at different types of dot positions. A variety of methods are applicable for the nozzle classification. One available method classifies the plurality of nozzles into the M nozzle groups that are sequentially aligned in a sub-scanning direction to be separated from each other. In another available method, the plurality of nozzles are sequentially allocated to the M element groups one by one along the sub-scanning direction