A data converting for red, green, blue, and white four colors, after a pixel extracts a minimum value of red, green, and blue by using a minimum-value extractor to be the white light data value of the pixel converted to red, green, blue, and white four-color system; and then calculates a difference values among colors red, green, and blue of the pixel. The difference values of three colors are added to the neighboring pixels or sub-pixels such that at the same time when the red, green, blue, and white four-color system increases the luminance of the image color, the hue and saturation of the image color can be compensated adequately so that the image color can be very close to the situation of the original red, green, and blue three-color system.