1. An image data output system comprising: first signal-receiving circuit means capable of receiving binary dot image information; first processing circuit means capable of signal-processing said binary dot image information received by said first signal-receiving circuit means, said first processing circuit means being arranged to be a module individually contained in a first individual unit; second signal-receiving circuit means capable of receiving multi-level dot information; second processing circuit means capable of signal-processing said multi-level dot information received by said second signal-receiving circuit means, said second processing circuit means being arranged to be a module individually contained in a second individual unit; and a coupling circuit means capable of coupling said first individual unit containing said first processing circuit means and said second individual unit containing said second processing circuit means so that the first individual unit may subject to binary dot image processing an output signal from said second processing circuit means.