To solve a problem that a decrease in resolution causes the quality of the image to be deteriorated with unevenness noticeable in a stepwise changing part of the contour part of the image when an image is formed by dots based on liquid droplets.

The dots of the contour part of a character or a fine linear image are changed to the dots Dp with a relatively higher brightness than the brightness of other dots, or the blank dots in the periphery of the contour part are changed to image dots, and these changed dots are made to be such dots Dps that has a relatively higher brightness and a smaller size than the brightness and the size of other dots.