Apparatus and method for driving a display device

An apparatus for driving a display device including a plurality of four color (a first color, a second color, a third color and a fourth color) pixels, the apparatus comprising:

• an input unit receiving input three-color (a first color, a second color and a third color) image signals;
• an image signal modifier converting the three-color image signals into output four-color image signals such that a gamma curve for achromatic color of the display device has no inflection point below about a 94 percent transmittance of the gamma curve, wherein the gamma curve is a relationship between a gray of one of the input three-color image signals and the transmittance of a-corresponding one of the four-color image signals;
• 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 (Max), a middle input gray (Mid), and a minimum input gray (Min), 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 fourth color image 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 fourth color image gray (W) as follows:
• when Γ(Max)>[s1/s1−1]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)], and
• when Γ(Max)≦[s1/s1−1]Γ(Min),
• Max′=Max;
• Mid′=Γ−1{s1[Γ(Mid)−Γ(Max)]+Γ(Max)];
• Min′=Γ−1{s1[Γ(Min)−Γ(Max)]+Γ(Max)];
• and
• W=Γ−1[(s1−1)Γ(Max)],
• wherein Γ is a gamma conversion function, Γ−1 is a reverse gamma conversion function, and s1 is a scaling factor.

A method for driving a display device including a plurality of four color (a first color, a second color, a third color and a fourth color) pixels, the method comprising:

• assigning order indices after comparing grays of the input three-color (a first color, a second color and a third color) image signals and determining a maximum input gray (Max), a middle input gray (Mid), and a minimum input gray (Min);
• gamma converting (Γ) and reverse gamma converting (Γ−1) the maximum input gray, the middle input gray, and the minimum input gray;
• obtaining a maximum output gray (Max′), a middle output gray (Mid′), a minimum output gray (Mid′), and an output fourth color image gray (W), from relations
• 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)],
• when Γ(Max)>[s1/s1−1]Γ(Min);
• obtaining a maximum output gray (Max′), a middle output gray (Mid′), a minimum output gray (Mid′), and an output fourth color image gray (W), from relations
• Max′=Max;
• Mid′=Γ−1{s1[Γ(Mid)−Γ(Max)]+Γ(Max)],
• Min′=Γ−1{s1[Γ(Min)−Γ(Max)]+Γ(Max)], and
• W=Γ−1[(s1−1)Γ(Max)],
• when Γ(Max)≦[s1/s1−1]Γ(Min);
• and
• generating four-color image signals having the maximum output gray, the middle output gray, the minimum output gray, and the output fourth color image gray according to the order given by the order indices, wherein s1 is a scaling factor.