Patent ID: 7773102

Claim:
An apparatus for driving a display device including a plurality of four color pixels, the apparatus comprising: an input unit receiving input three-color image signals; an image signal modifier converting the three-color image signals into output four-color image signals such that a maximum gray among an input R signal, an input G signal, and an input B signal of the input three-color image signals is equal to a maximum gray among an output R signal, an output G signal, and an output B signal of the output four-color image signals, and another gray of the output R signal, G signal, and B signal is derived from the maximum gray and at least one other gray of the input R signal, G signal, and B signal; and an output unit outputting the output four-color image signals, wherein the image signal modifier compares grays of the input three-color image signals, determines a maximum input gray, a middle input gray, and a minimum input gray, and assigns order indices based thereon, gamma and reverse gamma converts the maximum input gray, the middle input gray, and the minimum input gray to obtain a maximum output gray (Max′), a middle output gray (Mid′), a minimum output gray (Min′), and an output white gray (W) of the output four-color image signals, and generates the output four-color image signals based on the order indices, wherein the maximum input gray (Max), the middle input gray (Mid), and the minimum input gray (Min) have relations with the maximum output gray (Max′), the middle output gray (Mid′), the minimum output gray (Min′), and the output white gray (W) as follows: when Γ(Max)>[ s 1 / s 1 −1]Γ(Min), Max′=Max; Mid′=Max Γ −1 [Γ(Mid)−Γ(Min)]/[Γ(Max)−Γ(Min)]; Min′=0; and W =Max Min/Γ −1 [Γ(Max)−Γ(Min)], where Γ is a gamma conversion function, Γ −1 is a reverse gamma conversion function, and s 1 is a scaling factor, and wherein the maximum input gray (Max), the middle input gray (Mid), and the minimum input gray (Min) have relations with the maximum output gray (Max′), the middle output gray (Mid′), the minimum output gray (Min′), and the output white gray (W) as follows: when Γ(Max)≦[ s 1 / s 1 −1]Γ(Min), Max′=Max; Mid′=Γ −1 {s 1 [Γ(Mid)−Γ(Max)]+Γ(Max)]; and W=Γ −1 [( s 1 −1)Γ(Max)], where Γ is a gamma conversion function, Γ −1 is a reverse gamma conversion function, and s 1 is a scaling factor.