1. A method of displaying image data comprising a plurality of pixels each comprising at least two sub-pixels, the method comprising: setting at least two directions relative to a sub-pixel to be displayed and calculating differences of brightness values of at least two pixels or sub-pixels positioned in each of the set directions; selecting one of at least two of the differences and determining a reference direction indicated by the selected difference; selecting in the reference direction at least one sub-pixel or pixel neighboring the sub-pixel to be displayed; and filtering a brightness value of the sub-pixel to be displayed and a brightness value of the at least one sub-pixel or pixel which is selected and re-assigning the filtered brightness value to the sub-pixel to be displayed.