A multi-module device having first and second modules is disclosed. The first and second modules communicate through a serial bus. The first module has a memory for storing image data in a RGB format and a processing unit for converting the image data from the RGB format to a L*a*b* format, before outputting image data in the L*a*b* format through the serial bus. The second module receives the image data in the L*a*b* format, converts the image data to a CMY format and prints the image data in the CMY format.