To achieve an improvement in printing speed while preventing poor discharge of ink.
The side of a main controller is configured as follows. Gray scale data are extracted from in RGB data of resolution (600 dpi) matched with K so as to take out the gray scale data as K data and to transmit the K data to a sub controller 50. The remaining RGB data are converted into resolution (300 dpi) matched with CMY while the converted RGB data are converted into CMY data by a 3D-LUT. The converted CMY data are binarized by halftone processing so as to generate image data for CMY. The side of the sub controller is configured as follows. The received K data are binarized by halftone processing. If an ink discharge amount Q when discharging K ink by one pass is below a threshold Qref, image data for one pass are generated from the binarized data for one pass. If the ink discharge amount is larger than the threshold Qref, image data of each pass are generated by dividing the binarized data such that printing for one pass is executed by a plurality of passes.
Osamu Suzawa
Kazuhiko Miyasaka