In a printer for printing an image by a distribution of dots having different densities per unit area or dots having different hues, the structure of the present invention accurately determines the on/off state of the different dots and ensures high quality printing. Recording ratios Rn and Rt of deep dots and light dots corresponding to input tone data DS in a target pixel are read from a map representing the relationship between the recording ratios and the tone data. The systematic dither method is adopted to determine formation or non-formation of a deep dot in the target pixel. This method compares the recording radio Rn of deep dots with a threshold value Dref corresponding to the target pixel and read from a threshold matrix TM. In the case where a deep dot is not formed, the recording ratio Rt of light dots is corrected by adding the recording ratio Rn of deep dots and subsequently compared with the same threshold value Dref to determine formation or non-formation of a light dot in the target pixel. The structure of the present invention uses only one threshold matrix to realize desired recording ratios without causing any overlap of deep dots with light dots. This structure is also applicable to dots having different hues. In this case, one threshold matrix is used to determine the on/off state of dots having different hues without causing any interference of the different hues.