1. An image processing device comprising: a processor; and a memory storing computer-readable instructions therein, the computer-readable instructions, when executed by the processor, causing the image processing device to perform: acquiring target image data including each pixel value of a plurality of pixels, the target image data representing a target image by using the plurality of the pixels; extracting a plurality of edge pixels from the plurality of the pixels in the target image; determining a first reference value by using the plurality of edge pixels; generating correspondence data by using the first reference value; and converting, using the correspondence data, a plurality of original pixel values of the plurality of pixels into respective converted pixel values, the correspondence data including a first feature used to convert each of the original pixel values smaller than or equal to the first reference value, and a second feature used to convert each of the original pixel values greater than the first reference value, the first feature being different from the second feature.