1. An image processing device capable of generating coded image data, the coded image data representing an image to be printed in a printing apparatus, comprising: a data generator configured to downscale tone values of pixels included in the image in a halftoning process, the tone values of pixels being included in a predetermined scale range, and assign a plurality of types of codes having different lengths to the downscaled tone values to generate coded image data, which describes the downscaled tone values in the different types of codes; and a data transmitter configured to transmit the coded image data to the printing apparatus, wherein the data generator downscales the tone values of pixels in the image by classifying each tone value of pixels into one of segments, which are unevenly delimited by predetermined thresholds within the predetermined scale range inclusive of the tone values of pixels and include a larger segment and a smaller segment, and assigning a code with a shorter bit length to the tone value classified into the larger segment.