According to this invention, the image attribute is determined by determining whether the image of each color component of color image data having undergone a screen process is a continuous tone image, and whether the image of each color component is a pattern image. Whether to perform an interpolation process is determined for each color component based on the attribute determination result of each color component. If it is determined that the images of all the color components are pattern images, interpolation determination results do not coincide with each other, and there is a color component determined to represent a continuous tone image, the interpolation determination result of this color component is overwritten with the interpolation determination result of the remaining color components. The interpolation process is executed in accordance with the interpolation determination result.