An image processing device includes a controller. The controller specifies an edge pixel based on image data, and sets a target pixel and a reference pixel from among a plurality of pixels. The target pixel is located between the edge pixel and the reference pixel. The controller determines whether a determination condition is satisfied for the target pixel. The determination condition indicates that a pixel value of the edge pixel, a pixel value of the target pixel, and a pixel value of the reference pixel monotonically increase in said order. The controller sets a binary value of the target pixel to a first value without using a dither matrix when the determination condition is satisfied, and sets the binary value of the target pixel to one of the first value and a second value by using the dither matrix when the determination condition is not satisfied.