When dot density conversion processing of page data is effected by managing the position, size and data kind of each area for the page data including the portions which are formed as the data of different areas for at least two kinds of data of a plurality of data kinds each having at least one kind...http://www.google.fr/patents/US5493420?utm_source=gb-gplus-shareBrevet US5493420 - Dot density conversion method and system
