Method and apparatus for saving printer memory

A method for receiving, in a printer, printer commands representing a page and sending successive print engine commands describing the page to a print engine, comprising:

• providing a logical subdivision of the page into a plurality of regions;
• encoding the printer commands into a selected one of a set of representations for each region and storing the representation in a memory while monitoring the amount of memory used to detect memory overflow, where the selected representation is one of at least three distinct alternative representations;
• detecting as a problem region each region for which print engine commands cannot be generated on the fly from the representation selected for a region before the region is consumed by the print engine during printing;
• reacting to a detected memory overflow by changing the representation selection of one of the regions to a representation requiring less use of memory and re-encoding the one of the regions according to the changed selection;
• reacting to a detected problem region by changing the representation selection of the problem region to a representation requiring less time to generate print engine commands and re-encoding the problem region according to the changed selection;
• and
• generating printer commands from each of the regions when all the regions have been encoded and sending the generated printer commands to the print engine.

A computer program, residing on a computer-readable medium, for receiving in a printer a sequence of page description language commands describing a page and for sending a sequence of raster scanlines describing the page to a print engine, comprising instructions for causing the printer to:

• convert the page description language commands for the page to display list commands;
• associate each display list command with a region of the page;
• store display list commands in a memory;
• rasterize the display list commands of a region and store the resulting rasterized region data as uncompressed raster data in the memory;
• rasterize the display list commands of a region and store the resulting rasterized region data with lossless compression as lossless compressed raster data in the memory;
• rasterize the display list commands of a region and store the resulting rasterized region data with lossy compression as lossy compressed raster data in the memory;
• decompress compressed raster data from the memory, add data rasterized from a display list command, recompress the result, and store the compressed result into the memory;
• detect a region as a problem region, for which the region display list commands cannot be rasterized on the fly before the print engine will consume the raster data of the region during printing;
• detect a memory overflow during the storing of display list commands or during the storing of raster data;
• react to the detection of a problem region by invoking instructions to rasterize and compress the region;
• react to the detection of a memory overflow by selecting a form of storage requiring less memory for a region and invoking instructions to use the selected form, where the selection is made from alternatives including display list commands, uncompressed raster data, lossless compressed raster data, and lossy compressed raster data;
• and
• generate raster scanlines from display list commands, from uncompressed raster data, from lossless compressed raster data, and from lossy compressed raster data to send to the print engine.

A printer having an input for receiving a page of data in the form of page description language commands, a print engine for printing pages composed of a predetermined sequence of raster scanlines received at a predetermined rate, and a raster generator for converting the received page description language commands into a sequence of raster scanlines in a format required for printing, the raster generator comprising:

• a memory;
• a convertor for converting the page description language commands received at the input into display list commands;
• means for logically dividing the page into a plurality of regions and associating each display list command with a region of the page;
• means for determining the amount of time to rasterize each region;
• means for determining if the memory is full;
• means for determining for each region whether to rasterize the region to the print engine on the fly, to pre-rasterize the region and store it as raster data, to pre-rasterize the region, compress it and store it as lossless compressed raster data, and to revert the lossless compressed raster data to a lossy compressed version of the pre-rasterized version, based on the time estimates for rasterizing each region and available space in the memory such that the page is rasterized on the fly to meet the predetermined rate while memory is conserved.

A raster generator having an input for receiving page description language commands, the raster generator for converting the received page description language commands into a sequence of raster scanlines in a format required for outputting according to a predetermined rate, the raster generator comprising:

• a convertor for converting the page description language commands received at the input into display list commands;
• associating each display list command with a region of the page selected from a set of regions that subdivides the page;
• means for determining the amount of time to rasterize each sublist and for detecting any sublist that will not be able to be rasterized fast enough on the fly to satisfy the predetermined rate;
• means for determining if the memory is full;
• a convertor for converting the display list commands into an alternative format that may be rasterized fast enough to satisfy the predetermined rate if a sublist cannot be rasterized on the fly and for converting the display list commands into an alternative format that frees up memory space if memory is full;
• and
• means for storing the alternative format whereby throughput is assured and memory is conserved by transforming display list commands into an alternative format if a sublist would not be able to be rasterized on the fly to meet the predetermined rate and when memory is full.

A raster generator having an input for receiving page description language commands associated with a page to be printed, the raster generator for converting the received page description language commands into a sequence of raster scanlines in a format required for outputting according to a predetermined rate, the raster generator comprising:

• a first convertor for converting the page description language commands received at the input into a display list command format;
• a memory including one or more sublists for storing display list commands;
• means for determining if the memory is full;
• a second convertor for converting display list commands into a different alternative format that will free up memory;
• means for determining if converting subsequent page description language commands associated with the page into a display list command format will cause the memory to become full;
• and
• a third convertor for converting the display list commands in the alternative format into a third format that will free up memory, the third format being different from both the alternative format and the display list command format.

A method for receiving in a printer a page representation incorporating a sequence of page description language commands and sending a sequence of raster scanlines describing the page to a print engine, comprising:

• converting the page description language commands to display list commands;
• associating each display list command with a region of the page selected from a set of regions that subdivides the page;
• encoding each region of the page into a selected one of a set of representations and storing the representation in a memory while monitoring the amount of memory used in order to detect memory overflow, where the set of representations comprises display list commands, uncompressed raster data, lossless compressed raster data, and lossy compressed raster data;
• identifying a region as a problem region when representation for the region cannot be rasterized on the fly before the print engine will consume the region during printing;
• reacting to a detected memory overflow by changing the selection of one of the regions of the page to a representation requiring less use of memory and re-encoding the one of the regions according to the changed selection;
• reacting to the detection of a problem region by changing the selection of the problem region of the page to a representation which is able to be rasterized on the fly and re-encoding the region according to the changed selection;
• and
• generating raster scanlines from each of the regions and sending them to the print engine.

A method of reducing the memory requirements for a printer that receives a page description language representation of a page to be printed, the method comprising:

• converting page description language commands for the page into a display list command format;
• storing display list commands in one or more sublists of a memory;
• determining if the memory is full;
• converting display list commands into a different alternative format that will free up memory;
• determining if converting subsequent page description language commands associated with the page into a display list command format will cause the memory to become full;
• and
• converting the display list commands in the alternative format into a third format that will free up memory, the third format being different from both the alternative format and the display command format.