An image data processing method and device are disclosed. The method comprising: receiving a first display data combination, the first display data combination comprises red, green, and blue sub-pixel display data; transforming the first display data combination into a second display data combination, the second display data combination comprises red, green, blue, and white sub-pixel display data; transforming the second display data combination into a third display data combination, the third display data combination comprises any three of the red, green, blue, and white sub-pixel display data. The disclosed method can raise image contrast.