1. An image processing apparatus for processing data used for printing an image on a print medium with use of printing materials of multiple colors including at least printing material of a first color, printing material of a second color different from the first color, and printing material of a third color having higher lightness than the first and second colors, the image processing apparatus comprising: one or more processors; and one or more computer-readable media coupled to the one or more processors, the one or more computer-readable media storing instructions that, when executed by the one or more processors, cause the image processing device to perform operating comprising: acquiring first, second, and third pieces of multivalued data respectively corresponding to the printing materials of the first, second, and third colors; and generating first, second, and third pieces of quantization data, respectively corresponding to the printing materials of the first, second, and third colors, for a plurality of pixels by quantization processing using a plurality of threshold value matrices defining threshold values for respective pixels, wherein the generating, (i) generates the first quantization data on a basis of the acquired first piece of multivalued data of a target pixel and a threshold value for the target pixel in a first threshold value matrix, without using a second threshold value matrix, the arrangement of threshold values in the first threshold value matrix being different from the arrangement of threshold values in the second threshold value matrix, (ii) generates the second quantization data on a basis of the acquired second piece of multivalued data of the target pixel and a threshold value for the target pixel in the second threshold value matrix, without using the first threshold value matrix, and (iii) generates the third quantization data on a basis of the acquired third piece of multivalued data of the target pixel, the threshold value for the target pixel in the second threshold value matrix and the second piece of multivalued data of the target pixel.