A method is provided which is intended to reduce a visibility of ink dots ejected onto a print medium during a preliminary ejection operation to produce a satisfactory printed image. Preliminary ejection data is compared with image data. When the preliminary ejection necessary to performed on a pixel that has no image data, image data of a pixel close to the pixel being processed is searched. When image data exists, the image data is moved to a pixel that has preliminary ejection data. The preliminary ejection data is added to the image data one scan at a time to perform printing.