Patent ID: 7483011

Claim:
An apparatus of converting input three-color image signals into four-color image signals including a white signal and output three-color signals, the apparatus comprising: a value extracting unit that extracts a maximum input and a minimum input among a set of input three-color image signals; an area determining unit that determines which of scaling areas the set of input three-color image signals belong to on the basis of the maximum input and the minimum input; and a four-color converting unit that converts the set of input three-color image signals into a set of four-color signals depending on the area determination, wherein the scaling areas includes a fixed scaling area and a variable scaling area, and the four-color converting unit performs fixed scaling with a fixed scaling factor when the set of input three-color image signals belongs to the fixed scaling area and performs variable scaling when the set of input three-color image signals belongs to the variable scaling area depending on the set of input three-color image signals.