The present disclosure provides an image processing method, an image processing device, and a display device. The image processing method includes: acquiring image data including display data of all of pixels of an image; and performing, on the display data of each of the pixels, operations of: determining Euclidean distances from the display data of the pixel to the display data of a first pure color, the display data of a second pure color, and the display data of a third pure color in a set color space; and replacing the display data of the pixel with one of the display data of the first pure color, the display data of the second pure color and the display data of the third pure color according to the determined Euclidean distances and a preset rule.