Method and apparatus for building rasterized lines of bitmap data to be

Abstract

An improved printer is provided that receives a print job from a host computer and divides the bitmap image of a page to be printed into a series of image blocks or tiles. Each image block containing non-null data will be stored in the printer's memory system, typically placed in a non-contiguous memory location with respect to other blocks. The null image data blocks will not be stored in the printer's memory system, but instead only their locations on the physical printed page will be stored in a 'block list table.' Each entry in the block list table contains the beginning address of the physical RAM area that contains one of the image data blocks, and also contains other variables or attributes concerning the particular image data block, such as whether or not this block is a regular non-null data block, or a 'no-op' (or 'NOP') block containing null data. Null data blocks require no physical memory address to be listed in their entry on the block list table, since no physical RAM areas are needed for storing null bitmap image data. Rather than building a band buffer in contiguous memory before shipping rasterized data to the laser printhead, the present invention builds in a cache a series of rasterized line segments of bitmap data in real time and sends them to the laser printhead 'on the fly,' by retrieving a single rasterized line segment of data, block-by-block, as needed to complete a single entire line.