To record a multi-valued image by an ink-jet head, an ink droplet is jetted from a recording element (nozzle) for the number of times corresponding to the density of a pixel to be reproduced. Accordingly, the pixel data to determine the number of ink-jet operation is expressed by a plurality of bits...http://www.google.com.au/patents/US5975670?utm_source=gb-gplus-sharePatent US5975670 - Recording apparatus for gradation recording
