1. A data conversion unit in a display device comprising: a color analysis portion configured to determine presence of a pure color component in an input image by analyzing R (red), G (green) and B (blue) components of RGBW (red, green blue and white) data signal, wherein the input signal is included the RGBW data signal; and a brightness adjustment portion configured to adjust brightness of W (white) component in the RGBW data signal according to a hue of the pure color component present in the input image, wherein the color analysis portion includes a hue distribution analyzer configured to compare a saturation of each pixel of the input image obtained from the RGB data signals against a first reference value to determine the presence of the pure color component, wherein the color analysis portion further includes a hue distribution quantity analyzer configured to compare a number of pixels having the saturations of at least the first reference value against a second reference value, the hue distribution quantity analyzer determining that the input image includes the pure color component when the number of pixels having the saturation is at least the second reference value.