An image processing device comprises a processor and a memory. The processor executes computer-readable instructions stored in the memory. The instructions cause the image processing device to acquire target image data including each pixel value of a plurality of pixels. The instructions cause the image processing device to extract a plurality of edge pixels from the plurality of the pixels in the target image. The instructions cause the image processing device to determine a first reference value by using the plurality of the edge pixels. The instructions cause the image processing device to generate correspondence data by using the first reference value. The instructions cause the image processing device to convert, using the correspondence data, a plurality of original pixel values of the plurality of pixels into respective converted pixel values.