Patent US 5,282,269

A raster image memory which serves as a bit-map memory for the storage of the bit representation of a whole page to be printed for a raster output scanner is connected to a raster image processor by a synchronous raster image bus having a number of data and modification code lines. Each memory element of the bit-map memory corresponds to a position on the page. The raster image processor fills the raster image memory. A logic processing unit is disposed between the raster image bus and the bit-map memory so that one input of the logic processing unit is connected to the data lines of the raster image bus and another input of the logic processing unit is connected to the data outputs of the bit-map memory. The logic processing unit is also capable of performing a number of logic operations on the data presented at the inputs of the logic processing unit in response to the signals on the modification code lines.