A system and method of processing a component color image signal extracted from image signals are disclosed, including a quantizing unit for quantizing the component color image signal over a plurality of quantization regions of the component color image signal, such that the color difference per unit error caused by quantization of the component color image signal in each of the plurality of quantization regions is within a predetermined value. This quantizing unit operates also to quantize the component color image signal under a quantization level number different for each of regions specified by the value of the component color image signal, as a threshold, corresponding to either the polarity change or the maximum of the component color image signal.