Patent ID: 8405675

Claim:
A method for converting three color values to four color values, comprising: obtaining a first color value, a second color value and a third color value of a pixel; calculating a first difference value between the first color value and the second color value, a second difference value between the second color value and the third color value and a third difference value between the third color value and the first color value; generating a first color converting value, a second color converting value, a third color converting value and a fourth color converting value according to the first color value, the second color value and the third color value if the first difference value, the second difference value and the third difference value are lower than a threshold value, and now the fourth color converting value being greater than zero; and generating the first color converting value, the second color converting value, the third color converting value and the fourth color converting value if one of the first difference value, the second difference value and the third difference value is greater than the threshold value, and now the fourth color converting value being zero, and the first color converting value, the second color converting value and the third color converting value being respectively equal to the first color value, the second color value and the third color value.