The low and high occupancy rate matrix sets are stored in the inkjet printer which performs printing with dots having different sizes. For the original image where banding unevenness easily appears, used is the low occupancy rate matrix set where the occupancy rate of all dots is lower than 100% in the maximum value of gray level and the proportion of the large dots is high in a high range of gray level. For the original image where reproducibility of details is required, used is the high occupancy rate matrix set where the occupancy rate of all dots becomes 100% in a value of gray level lower than the maximum value of gray level and the proportion of the small dots is high in a middle range of gray level. It is therefore possible to perform appropriate printing in accordance with the classification of the original image.