Facsimile and static presentation processing – Static presentation processing – Communication
Reexamination Certificate
1997-09-05
2001-02-06
Popovici, Dov (Department: 2722)
Facsimile and static presentation processing
Static presentation processing
Communication
C358S001200
Reexamination Certificate
active
06184997
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a page printer, a resolution converting method, and a variable-length reversible compression process, and more particularly, to a page printer such as a laser printer and an LED printer, a resolution converting method for achieving high image quality while reducing a memory capacity, and a variable-length reversible compression process for a bi-level image. The present invention is also directed to a printer part of a digital copy machine.
2. Description of the Related Art
Recently, resolution of a page printer such as a laser printer is increasing, and at present, a page printer of 600 dots/inch (DPI) is widely used. Therefore, a memory capacity of a frame buffer (page memory) in the page printer needs to be approximately 4 MB for an A4 paper with 600 DPI, and approximately 8 MB for an A3 paper with 600 DPI. Such increases of the memory capacity of the frame buffer have a large influence on product cost. However, the cost of the page printer is currently decreasing. Therefore, it is necessary to prevent the cost of the page printer from increasing due to improvement of the resolution.
For a reversible compression technique for bi-level image data, a variety of compression schemes are used. Widely used compression schemes include a modified Huffman (MH) coding scheme (one-dimensional compression scheme), a modified READ (MR) coding scheme (two-dimensional compression scheme), and a modified MR (MMR) coding scheme, which are used in a facsimile, etc., and a Lempel-Ziv (LZ) scheme which is usually used for a text file and a binary file in a computer. Furthermore, recently, a JBIG scheme using arithmetical coding which is internationally standardized is also used.
However, since these reversible compression techniques for the bi-level image data carry out a sequential coding process in sequence from a top of the image or the file, it is difficult to process only a desired area of the image or the file in real time.
In the computer, information of the image or the file is formed by a plurality of image information which are produced in selected areas on a CRT in sequence. Some of the image information may be produced in the same area as in a case of multiple windows. When the plurality of image information are transmitted to the page printer to be printed, they are transmitted in an order of the image information being sequentially produced. Therefore, to timely compress the plurality of the image information in the page printer, the image information in the desired area should be processed earlier. Accordingly, it is difficult to directly use the above-mentioned compression techniques for the page printer.
In other methods disclosed in publications “PCL 5 Comparison Guide for Printers”, Hewlett Packard No. 5961-0999, first edition, May, 1993, and “SoftBand (registered trade mark) High-Performance Low-Memory Imaging”, Proprietary Information, Phoenix Technologies Ltd., in the computer or the page printer, the plurality of image information are converted to a format which can be processed in sequence from a top of the file, whereby the above-mentioned compression techniques may be used. However, in this case, sometimes necessary memory capacity may overflow designed memory capacity, and, thus, the memory capacity may not be sufficiently reduced.
Further, at present, there is no fixed-length reversible compression technique for the bi-level image data in the world. Though the fixed-length compression technique may always reduce the memory capacity, this compression technique cannot recover an original resolution image (no reversible).
Accordingly, with the present compression techniques, any image data may not be compressed to a desired data amount.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a page printer. The cost of the printer can be reduced and the resolution of the printer can be improved while reducing the memory capacity of the frame buffer in the printer by using compression techniques.
It is another object of the present invention to provide a resolution converting method. By using the method, when bi-level image data is reversibly compressed by a block unit, even if the image data cannot be compressed to a desired data amount, the image data may be printed with an image quality level having a commonly-used resolution without increasing the memory capacity.
This permits the disadvantages described above to be eliminated.
The object described above is achieved by a page printer printing document data comprising: a first rasterizing part for rasterizing the document data with a first resolution; a data compression part for compressing each of blocks which form first rasterized data from the first rasterizing part to produce a compression code, and for storing the compression code in a compression memory; a data decompression part for decompressing the compression code stored in the compression memory, and for transmitting decompressed data to a printer engine having the first resolution; a second rasterizing part for rasterizing the document data again with a second resolution less than the first resolution when the compression code exceeds a given size; and a resolution converting part for converting second rasterized data from the second rasterizing part to conversion data with the first resolution, and for transmitting the conversion data to the printer engine having the first resolution.
According to the above-mentioned page printer, the document data to be printed is rasterized with the first resolution which is commonly used for printing, and is compressed. Therefore, a memory capacity may be reduced. Further, even if the document data cannot be compressed to a desired size, the document data is rasterized again with the second resolution less than the first resolution. The re-rasterized data is processed in the bi-level-to-multi-level conversion process. Therefore, this document data may be printed with the first resolution commonly used for printing.
The object described above is also achieved by a resolution converting method used in a page printer comprising the steps of: (a) carrying out a bi-level image area separating process for data which is rasterized with a second resolution; (b) carrying out a multi-level smoothing process for an area which is recognized as a character and line area to convert to a first resolution; (c) carrying out a quasi-multi-leveling process using a smoothing filter for another area which is not recognized as the character and line area to convert to multi-level data; and (d) converting the multi-level data in step (c) to data of the first resolution so as to print with the first resolution.
According to the above-mentioned resolution converting method, even if the document data cannot be compressed to a desired size, the document data may be printed with high resolution commonly used for printing by carrying out the resolution conversion according to kinds (image areas) of image data without increasing the memory capacity.
The object described above is also achieved by a variable-length reversible compression process for data compression of image data used in a page printer, the image data having a plurality of block units, each of which includes u block words in main and sub scanning directions, each of block words including t dots in the main scanning direction, the process comprising the steps of: (a) dividing a page buffer which is required for rasterizing the image data to a first resolution into several elements corresponding to the block units; (b) checking whether a content of one of the block units is all white, and storing a checking result in an m-bit white map table; and (c) preparing, when the content of the one of the block units is not all white, n-bit compression data tables for the u block words in an address area indicated by the white map table, and storing a result of compression process for each of the u block words in the n-bit compression data tables.
The object described above is a
Hanyu Yoshiaki
Shimomae Mutsuo
McDermott & Will & Emery
Popovici Dov
Ricoh & Company, Ltd.
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