Image data, or RGB luminance data input from a host computer, is color-converted by LUT into 8-bit CMYK density data for each ink color. The CMYK density data is divided into predetermined regions and, based on a gray scale value for each of the divided regions, ink application volumes are calculated. According to the calculated ink application volumes, the 8-bit processing liquid application data S is generated. Then, the CMYK density data and the processing liquid application data undergo output gamma processing, after which they are quantized by a quantization processing unit into 1-bit ejection data for each nozzle.