Printing system and method

Abstract

A image is printed from a source of drawing instructions. The image is reducible to pixels arranged in a plurality of ranked image lines. The system employs a storage device having compressed and uncompressed regions. Each region has a designated capacity and each is arranged to store pixels of one more of the plurality of image lines. A drawing processor is coupled to the storage device and can be coupled to the source of drawing instructions for responding thereto. This drawing processor can store new pixels in the storage device for successively selected ones of the image lines. The drawing processor has a conditional device, a decompression device and an insertion device. The conditional device can compressively encode and move from the uncompressed region to the compressed region, a remote one of the image lines, if: a) the selected one of the image lines is in the compressed region, and b) the uncompressed region has reached its designated capacity. The decompression device can expansively decode the selected one of the image lines, if located in the compressed region. The insertion device can insert one or more new pixels according to the drawing instructions into the selected one of the image lines by storing the selected one in the uncompressed region. The printing system also has a printing engine coupled to the storage device for printing the plurality of image lines in rank order, decompressing compressed ones of the image lines from the compressed region before printing.

Description

BACKGROUND OF THE INVENTIONThe present invention relates to printing systems and methods and, in particular, to apparatus and techniques for printing an image with a reduced need for memory.A laser printer can be a fairly complex device having a self-contained computer system, usually referred to as a microprocessor based controller. The controller can have a microprocessor, 1 Mb of read only memory (ROM) and 2 Mb of random access memory (RAM). In many installations, the personal computer driving the laser printer may be slower and have less memory than the printer. Moreover, some sophisticated laser printers may employ a hard disk for handling complicated, high definition images.Some laser printers include an interpreter that can respond to drawing commands such as: draw a line from point x.sub.1, y.sub.1 to point x.sub.2, y.sub.2. Even more sophisticated programming languages have been incorporated in ROM in some printers. Some fairly rich programming languages employ variables, l...

AI Technical Summary

Benefits of technology

In accordance with the illustrative embodiments, demonstrating features and advantages of the present invention, there is provided a printing system for printing from a source of drawing instructions a two dimensional image. This two dimensional image is reducible to pixels arranged in a plurality of ranked image lines. The printing system has a storage means with a compressed region and an uncompressed region. Each region has a designated capacity and each is arranged to store pixels of one or more of the plurality of image lines. The system has a drawing means coupled to the storage means and adapted to be coupled to the source of drawing instructions for responding thereto. This drawing means can store new pixels in the storage means for successively selected ones of the image lines. The drawing means includes a conditional means, a decompression means and an insertion means. The conditional means can compressively encode and move from the uncompressed region to the compressed region a remote one of the image lines, if a) the selected one of the image lines is in the compressed region and b) the uncompressed region has reached its designed capacity. The decompression means can expansively decode the selected one of the image lines, if located in the compressed region. The insertion means can insert one or more new pixels according to the drawing instructions into the selected one of the image lines, by storing this selected one in the uncompressed region. The printing system includes a printing means coupled to the storage means for printing the plurality of image lines in ranked order, decompressing compressed ones of the image lines from the compressed region before printing.

In the preferred embodiment, image lines are compressed only to the extent needed to free additional memory for writing new pixels. Accordingly, the region being drawn can remain uncompressed, so that processing occurs quickly.

When a particular band is selected, only relevant elements of the display list are executed and only to the extent they affect image lines inside the selected band. This technique is most effective when there are rather large vertical images. Otherwise, a series of commands to draw numerous vertical lines could require every line in the page to be compressed and uncompressed numerous times, once for each vertical line. The display list avoids this time consuming approach by working only with line segments for the current band, where all image lines can remain uncompressed.

Problems solved by technology

In many installations, the personal computer driving the laser printer may be slower and have less memory than the printer.

The compression ratio can be set arbitrarily high, but will eventually cause a loss of visual detail, which may or may not be acceptable depending upon the application.

With the process an image is normally assembled line by line, requiring the controller to revise image lines many times. The resulting difficulty is the large amount of time spent compressing and decompressing image lines as the image is assembled.

When all of the data is compressed at the computer and sent compressed to the printer, large amounts of memory are required at the computer, but not at the printer.

Requiring that the printer decompress every line of the image can slow the printing process unacceptably.

The difficulty with the banding approach is the need to completely map the next band before the prior band is done printing; otherwise the printer must stop.

Thus, for relatively complex images, the banding method is unsatisfactory for general application.

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