A data conversion unit is disclosed which includes: a transformation portion configured to transform R (red), G (green) and B (blue) sub-pixel data signals of input image data into R, G, B and W (white) sub-pixel data signals; and a brightness reinforcement portion configured to adjust brightness of a transformed W sub-pixel data signal included in the transformed R, G, B, and W sub-pixel data signals based on brightness distribution of the input image data.