1. A liquid crystal display, comprising: an RGBW panel having a plurality of data lines, a plurality of gate lines crossing the data lines, a plurality of TFTs connected to crossings between the data lines and the gate lines, and an RGBW pixel structure; an image conversion unit for converting white luminance Y of data displaying a white background into a value satisfying any one of the following equations upon detecting a brightness contrast image including a pure color image with the white background; a data driving circuit for converting digital data converted by the image conversion unit into positive/negative analog data voltages; and a gate driving circuit for supplying gate pulses to the gate lines, the equations including Y ( white ) = Yref ( white ) × MIN { Y ( yellow ) Yref ( yellow ) , Y ( cyan ) Yref ( cyan ) , Y ( magenta ) Yref ( magenta ) } , Y ( white ) = Yref ( white ) × Y ( yellow ) Yref ( yellow ) , and Y ( white ) = Y ( yellow ) wherein Y(X) is a luminance value of color X, Yref(X) is a luminance value of color X of a reference display device having an RGB pixel structure, and MIN Y(X, Y, Z) is the minimum luminance value among X, Y, and Z.