A signal processing method comprises the steps of: inputting three signals specifying a color of one pixel; and generating four signals from the input three signals, wherein each of said four signals represents intensities of four different colors to display a color of one pixel by mixing colors, wherein said generating step includes a first converting step of converting the input three signals to two signals representing intensities of two colors among the four colors and a signal representing intensity of a mixed color obtained by mixing (a) the four colors or (b) a plurality of colors among the four colors; and a second converting step of converting the signal representing intensity of the mixed color to a plurality of signals representing intensities of a plurality of colors including at least other two colors different from the two colors.