The present disclosure includes an image displaying method and a display device. The method includes: obtaining three-color sub-pixel data of each of pixels of a current image, wherein the three-color sub-pixel data includes a first red, green, blue grayscale value (R1, G1, B1) separately; obtaining a first white grayscale value (W1) in accordance with the three-color sub-pixel data; performing a color gamut mapping toward the four first grayscale values in accordance with a predetermined rule; performing a sub-pixel rendering process toward the four-color first grayscale values to obtain the updated three-colors sub-pixel data corresponding to each of the pixels; and outputting the updated three-colors sub-pixel data to the display panel. The RGB data of the current image may be converted to the image data that can be displayed on the four-color display panel so as to obtain a vivid display on the four-color display panel.