Facsimile and static presentation processing – Static presentation processing – Data corruption – power interruption – or print prevention
Reexamination Certificate
1997-07-01
2001-01-30
Zimmerman, Mark K. (Department: 2772)
Facsimile and static presentation processing
Static presentation processing
Data corruption, power interruption, or print prevention
C358S001120, C358S296000, C358S426010, C358S450000, C348S415100, C341S051000, C341S107000, C382S173000, C382S175000, C382S232000, C382S239000
Reexamination Certificate
active
06181435
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an image forming method and apparatus for forming an image on a print medium.
DESCRIPTION OF RELATED ART
Conventionally, an image forming apparatus, called a page printer such as a laser-beam printer, performs image formation while holding raster data for one page in a raster memory.
In recent years, the resolution of such image forming apparatus has been improved. In 600 dpi resolution, for example, a memory capacity of 4 MB is required for forming an image of one page of A4 size. Thus, the resolution is being greatly improved. Conventionally, one pixel has been represented by two levels (1 bit), however, the representation is being improved to 16 levels (4 bits) to 256 levels (8 bits), requiring an increasingly large capacity of raster memory.
To suppress the increase in cost due to the increase of memory capacity, various memory-saving techniques have been proposed.
For example, Japanese Patent Application Laid-Open No. 6-87251 discloses temporarily translating image data in page description language into coded raster representation as intermediate data, and storing the data represented in coded raster representation. In the coded raster representation, objects which were described in the page description language are objects such as “bitmap”, “run-length”, “trapezoid”, “box” and “fast boundary encoding bitmap” in a format which can be subjected to high-speed conversion to raster data, with data amounts less than the amounts of raster data. Note that the data translated into the coded raster representation is referred to “coded raster data”. Thereafter, upon printing, the coded raster data is transferred to a printing unit (printer engine), while being converted into raster data where dots are arranged in the order of raster scanning.
In this manner, the memory resource is saved by holding image data to be printed as coded raster data. However, in this method, there are possibilities that the processing time for rasterizing coded raster data is longer than time for transmitting data to the printer engine (this status is called “over-run”), and that coded raster data cannot be stored in a predetermined memory. To solve the inconvenience, memory requirement for these cases are predicted. If this technique is used, the resolution of an image as the object of printing and/or the tone-level representation is degraded, thus the necessary memory capacity and processing time are reduced.
However, this method degrades the quality of output image. Japanese Patent Application Laid-Open Nos. 4-323060, 6-233141 and 6-284297 propose to compress raster data for reducing memory capacity. Especially, Japanese Patent Application Laid-Open No. 6-233141 discloses temporarily converting data in page description language into intermediate data and storing the intermediate data. In a case where the memory capacity for storing the intermediate data is short, or processing for generating the raster data from intermediate data is complicated and it takes too much time, the raster data is generated and compressed prior to printing.
However, compressing, especially lossless compressing provides variation in compression ratio, therefore, the size of compressed data is unknown before compression. Accordingly, this prior art requires processing such as garbage collection upon each data compression on all the available memory areas to generate a series of available areas, or processing for dividing the memory into cells and linking the cells to manage the set of cells as a continuity of virtual available memory areas.
The former processing must perform the garbage collection for each data compression, which causes overhead in processing time for memory rearrangement, thus degrading the overall performance. The latter processing causes memory overhead for link structure or for writing/reading data.
Further, upon expansion of compressed data, there is no problem if the expansion speed is faster than the time for transmitting data to the printer engine; however, in use of complicated compression method, the expansion speed cannot follow data transmission time, which causes over-run.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above conventional techniques, and has its object to provide an image forming method and apparatus which reliably performs image formation without causing over-run.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.
REFERENCES:
patent: 5299027 (1994-03-01), Nakamura et al.
patent: 5479587 (1995-12-01), Campbell et al.
patent: 5504842 (1996-04-01), Gentile
patent: 5506944 (1996-04-01), Gentile
patent: 5539865 (1996-07-01), Gentile
patent: 5544290 (1996-08-01), Gentile
patent: 5680521 (1997-10-01), Pardo et al.
patent: 5689589 (1997-11-01), Gormish et al.
patent: 5832126 (1998-11-01), Tanaka
patent: 510923 (1992-10-01), None
patent: 4-323060 (1992-11-01), None
patent: 6-87251 (1994-03-01), None
patent: 6-233141 (1994-08-01), None
patent: 6-284297 (1994-10-01), None
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Sealey Lance W.
Zimmerman Mark K.
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