An image data processing method and a device thereof are disclosed, and the method includes: receiving and executing a gamma correction process for first red, green and blue sub-pixel image data to obtain second red, green and blue sub-pixel image data; generating a first white sub-pixel image data, and third red, green and blue sub-pixel image data according to the second red, green and blue sub-pixel image data; and obtaining fourth red, green and blue sub-pixel image data and a second white sub-pixel image data through an inverse gamma conversion process.