Device and method for converting three color values to four color values

A device and a method for converting three color values to four color values are provided. In the method, a first to a third color values of a pixel are obtained. Further, a first to a third difference values between every two of the first to the third color values are respectively computed. If all of the first to the third difference values are lower than a threshold, a first to a fourth color converting values are generated according to the first to the third color values, and the fourth color converting value is higher than zero. On the contrary, the fourth color converting value is zero, and the first to the third color converting values are equal to the first to the third color values, respectively. Thereby, a color break-up can be suppressed, and color saturation can be maintained.