Patent US 4,739,397

An image processing system is specifically designed to process digital image data of different types, for example, by processing digital image data to print a monochromatic image with a color image printer, and includes color and monochromatic image data transmitters for transmitting digital image data such as color image data and monochromatic image data along with command data relating to an image reproduction mode. An electronic circuit is used to discriminate command data transmitted. The digital image data is processed in accordance with the discriminated command data. The command data is transmitted through a single channel to a processing apparatus sequentially before the transmission of the digital image data. In another aspect, transmitted digital color image data may be converted into digital monochromatic image data on the basis of a relative luminosity correction coefficient. A monochromatic image may thereby be produced from either transmitted monochromatic image data or the converted digital monochromatic image data.