shown in fig8 the detailed steps of the printing task are as follows 1 initializing wherein all the bands which are marked as bands to be pretreated are pre rasterized 2 setting up an auxiliary task if there is any complicated band which has not been pretreated wherein the complicated band which has not been pretreated is rasterized in the auxiliary task the main printing task has a higher priority than the auxiliary task so the auxiliary task can be only run when the main printing task is idle 3 rasterizing band 1 and transmitting the bitmap to a print buffer and starting a print engine 4 printing the band which is currently in the print buffer and 5 judging whether this band being printed is the last band and ending printing if yes otherwise judging whether the next band is a simple band the next band is rasterized till the start timing of its rasterization if the next band is a simple band and the raster bitmap are transmitted to the print buffer if the next band is not a simple band it is further judged whether the next band is a pretreated complicated band if it is true the raster bitmap from.