When a sum of a first gradation data for a first color and a second gradation data for a second color is greater than the maximum value of thresholds of a first threshold matrix, a generation unit generates a first overlapping gradation data and second overlapping gradation data by dividing a value obtained by subtracting the maximum value from the sum. Further, the generation unit generates a first quantization data based on a result of comparing the first overlapping gradation data with the second threshold or a result of comparing a difference between the first gradation data and the first overlapping gradation data with the first threshold, and generates a second quantization data based on a result of comparing the second overlapping gradation data with the first threshold or a result of comparing a difference between the second gradation data and the second overlapping gradation data with the second threshold.