Image analysis – Image compression or coding
Reexamination Certificate
1996-09-24
2001-07-31
Couso, Jose L. (Department: 2624)
Image analysis
Image compression or coding
C382S305000
Reexamination Certificate
active
06269190
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to processes and apparatus for processing image data, including combinations of text, graphics, and other images. More particularly, the present invention is related to techniques for reducing buffer memory requirements for such processes and apparatus.
BACKGROUND OF THE INVENTION
Most computer systems use a form of raster image to output image data to a visual output device such as a cathode ray tube (CRT) monitor, liquid crystal display (LCD), or a printer such as a color laser copier. A raster image is represented as a series of scan lines of pixels, wherein each pixel is accessed in a sequential manner, and each scan line is processed. An area to which image data may be output sequentially by the visual output device is referred to as a page. The image data of a page provides its complete visual representation.
Interpreters of page description languages typically process images in one or both of two modes: band mode and frame mode. In band mode, the entire page description is read, and a list of every imaging operation, called a display list, is built including all the data needed to image the page. Since all of the data also may include very large scanned images, a display list can grow to be very large. Scanned images require that the display list be temporality stored on secondary storage, with a performance reducing step required both to read and write. A fundamental advantage, however, is that the output frame is only traversed once, which permits lower speed devices to be connected with a minimum of buffering.
Frame mode on the other hand, does not include constructing a display list. Instead, a full image exists, and as each imaging operation is encountered, it is immediately processed to update the fill page image. Scanned images are also processed immediately, eliminating the problem of temporarily storing them. Thus, whereas band mode traverses the output page image in an orderly fashion, sweeping from one edge to the opposite edge, frame mode accesses the output page randomly.
Both of these however generally require a buffer memory which can hold the entire visual representation of a page. This memory is referred to as a frame buffer. Because of the large memory requirements for representation of a page, particularly with color laser copiers and color images, it is desirable to reduce the buffer memory requirements, for example by using some form of compression.
One compression method is shown in U.S. Pat. No. 5,506,944 to Ronald S. Gentile. This reference shows a system in which an image is divided into several regions. A page description, describing objects to be placed on the page, is ordered so that commands for each region are processed together. The regions are processed sequentially. A single memory element capable of storing the image data of an entire region in an uncompressed form is provided. After each region is processed, its corresponding image data is stored in a stack (a last-in, first-out buffer) in compressed format. When a page has been completely processed, this compressed image data is then read out of the stack to be decompressed and output to a printer.
A problem with this system however is that it requires a page description to be completely processed or ordered before processing of the frames can begin. It does not display operations to be processed in an arbitrary order. Additionally, it may suffer from the same problems as band mode operation when the display list becomes too large.
SUMMARY OF THE INVENTION
In the present invention, a page of an image is divided into several regions. Each of these regions may be compressed according to a different technique according to the kind of data within the region. In the proffered embodiment, the regions are fixed in equal sizes in an N×M matrix, but they need not be for purposes of the invention. Data for each region is available at any time and can be randomly accessed. Display operations may be processed in any order. For each display operation, the region which is affected, is uncompressed and processed. As other regions are processed, memory space is made available by compressing data in currently unused regions.
By using this kind of representation of a page and method of processing display operations, each region can be represented independently and differently. Each region can be compressed with a method that works well for the data contained in that region. Compression is used to reduce the memory requirements. Because display operations can be processed in any order, regions may be processed by multiple imaging systems functioning in parallel. Additionally, representations of regions on a page can be stored, transmitted, or used in different locations at different times.
Accordingly, one aspect of the present invention is a computer system and computer-implemented process for generating a representation of a document image. A representation of a document is generated, wherein the representation includes an indication of a plurality of regions into which the document is divided, compressed image data for each region and an index indicating a storage location of the compressed image data for each region. Indications of operations for generating the document image are received. For each operation, the representation of the document image is processed so as to add image data to the representation. Such processing involves identifying each region affected by addition of image data according to the indicated operation, decompressing the compressed image data of the identified region, and modifying the decompressed image data according to the indicated operation.
Another aspect of the invention is a digital nonvolatile computer-readable data recording medium for storing a representation of a page of a document comprised of a plurality of regions. The representation defines a list of region descriptions on the nonvolatile computer-readable data recording medium, wherein each region description includes an indication of a compression mode used to generate the compressed image data of the region, and an address indicating a storage location of the compressed data. For each region, compressed image data is defined at the storage location on the nonvolatile computer-readable data recording medium.
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Mikkelsen Carl
Speciner Michael
Couso Jose L.
Do Anh Hong
Electronics For Imaging, Inc.
Glenn Michael A.
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