An image is recorded on a recording medium by recording dots of a black ink and a color ink discharged onto the recording medium from a recording head. A boundary proximity-degree detecting circuit detects the degree of positional proximity, i.e., closeness, between the recording dots of the black ink and the recording dots of the color ink at the boundary between these dots. A dot substituting circuit performs, in accordance with the detected degree of positional proximity, substitution of the black pixels with recording dots of a color ink at the boundary. Thus, pixels of the image to be recorded are replaced with recording dots of a color ink by an extent which is determined based on the degree of positional proximity between the pixels of the different colors. A sharp black image can be obtained with minimized color mixing at the boundary between the black image region and the color region, regardless of the degree of positional proximity between these regions.