In ink-jet printing apparatuses having a monochrome head which is longer than a color head, if a monochrome image is processed as a color image, the printing speed cannot be improved. Accordingly, the color attribute is determined by pixel based on a luminance signal indicating a color multivalue image, and the number of color attributes and the number of array attributes in a first line group are counted. Based on these count values, a parameter indicating an image characteristic of second line group including the first line group is calculated. The image attribute of the second line group is determined in correspondence with the respective count values and the parameter. Then, based on the results of determination about adjacent second line groups, the image attribute of third line group included in the second line groups is determined. Thus attribute determination can be appropriately performed in predetermined band units of image data.