Image analysis – Image compression or coding – Adaptive coding
Reexamination Certificate
1998-12-23
2004-08-03
Do, Anh Hong (Department: 2624)
Image analysis
Image compression or coding
Adaptive coding
C382S232000, C382S233000
Reexamination Certificate
active
06771827
ABSTRACT:
This application includes Appendix A containing computer code that performs compression of image data in accordance with this invention and Appendix B containing computer code that performs decompression of image data in accordance with this invention.
A portion of the disclosure of this patent document contains material which is subject to (copyright or mask work) protection. The (copyright or mask work) owner has no objection to the facsimile reproduction by any-disclosure, as it appears in the Patent and otherwise Office patent file or records, but otherwise reserves all (copyright or mask work) rights whatsoever.
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates generally to compression and decompression systems and methods. More specifically, this invention relates to compression and decompression systems and methods that compress and decompress image areas containing edges of marks to be rendered in image data based on the direction of the edges of the marks.
2. Description of Related Art
The human viewer appreciates viewing non-continuous toneart information, e.g., text and/or lineart, at higher spatial resolutions than the spatial resolutions required for continuous toneart information, e.g., halftone information, because the human eye sees contrast information at a higher spatial resolution than color information. Therefore, more spatial resolution is necessary to render non-continuous tone regions than is necessary to render continuous tone regions. This differentiation between the amount of information necessary for the human eye to process non-continuous tone regions and to process continuous tone regions is due to hyperacuity. Hyperacuity is the human visual system's ability to differentiate locally misaligned edges of marks in a rendered image to a much finer extent than the receptor spacing of the human eye. It is not the frequency response, i.e., resolution, of the visual system, but the ability to reckon edge position with high precision that is most important.
Data transmitted in a bytemap, i.e., one byte for each pixel of the image, typically has a corresponding spatial resolution that is roughly equal to the size of the pixel. Forming high quality continuous tone regions does not require as much spatial resolution for the transmitted data. However, continuous tone regions require a high number of tone levels to minimize contouring, or the ability of the visual system to see changes in tone. In contrast, forming extremely detailed non-continuous tone marks, such as three or four point text, requires a significant amount of spatial resolution for the transmitted image data, but generally requires fewer number of tone levels.
In this case, the non-continuous tone pixels are not necessarily binary, but can also be composed of a number of gray levels. The non-continuous tone data is of the type that might be scanned in from a high quality scanner, or of a type called antialiased, which contains partial intensities to help in the removal of stairstepping or the positioning of edges.
Therefore, in a bytemap, high spatial resolution, e.g., 800×800 pixels per inch (ppi) is necessary for non-continuous tone regions, while continuous tone regions only need low spatial resolution, e.g., 400×400 (ppi). Therefore, transmitting bytemapped image data with high spatial resolution results in an unnecessary degree of spatial resolution for rendering continuous tone data and a waste of image system resources to process the unnecessary data.
If bitmaps are used instead to transmit image data for printing, continuous tone data is sent as prehalftoned dot shapes. Sending proper pre-halftoned dots to a destination, e.g., a printer, requires a high spatial resolution, e.g., 600×4800 ppi, to avoid contouring. However, 4800 pixels per inch resolution is too much resolution for non-continuous tone data.
Therefore, when using bitmaps, higher spatial resolution is necessary for rendering continuous tone data than is necessary for rendering non-continuous tone data, once again resulting in a waste of image system resources to process the unnecessary data.
SUMMARY OF THE INVENTION
Regardless of whether the bitmaps or bytemaps are used to render images, spatial resolution mismatch results because of the different requirements for rendering non-continuous tone data and continuous tone data. Nevertheless, conventionally, continuous tone data, e.g., halftone data, and non-continuous tone data, e.g., text and lineart data, are sent to a printer or associated hardware that convert bytemaps or bitmaps into scanning laser modulations at essentially the same spatial resolution.
Thus, this invention provides compression and decompression systems and processes for compressing and decompressing image data taking the resolution mismatch into consideration. In one exemplary embodiment of the compression and decompression systems and methods, regions of an image are optimally compressed and decompressed based on the composition of the regions, for example, whether the regions are continuous tone or non-continuous tone regions.
This invention separately provides compression and decompression systems and methods that at least double the spatial resolution for non-continuous tone data, while maintaining adequate spatial resolution for continuous tone data and minimizing the amount of memory and corresponding transmission bandwidth requirements.
The invention separately provides compression and decompression systems and methods for storing extra resolution in a frequency spatial resolution direction of non-continuous tone data to improve the appearance of an image rendered using the data.
The invention separately provides compression and decompression systems and methods that eliminate spatial resolution mismatch between data used to render continuous tone regions and data used to render non-continuous tone regions.
This invention separately provides compression and decompression systems and methods that provide the necessary information to provide high spatial resolution non-continuous tone data and low spatial resolution continuous tone data as compressed data.
The invention separately provides compression and decompression systems and methods that increase non-continuous tone data spatial resolution.
The invention separately provides compression and decompression systems and methods that render gray level information for two non-continuous tone pixels in a single byte.
The invention separately provides decompression systems and methods that typically double the spatial resolution of non-continuous tone data relative to the compressed data. That is, during compression, the compressed data is abbreviated in the high frequency spatial resolution direction, i.e., the directed acuity direction, which is the direction perpendicular to the edge.
According to the compression and decompression systems and processes of this invention, a bytemap is asymmetrically compressed and decompressed. During compression, either a low spatial resolution or high spatial resolution bytemap is divided into data blocks and segmented so that the continuous toneart data regions are separated from the non-continuous tone data regions. The segmented bytemap data is processed to provide both low spatial resolution continuous tone data and high spatial resolution non-continuous tone data.
Specifically, the high spatial resolution non-continuous tone data is compressed by quantizing and packing high resolution pixels in a direction across the edge, i.e., perpendicular to an edge of a mark to be rendered, and discarding high resolution pixels along the edge, i.e., parallel to the edge. Additional information, called tag bits, indicating the directions of the edges, e.g., vertical or horizontal directions, and the type of image data, e.g., continuous or non-continuous data, is also stored to enable decompression.
Subsequently, during decompression, the non-continuous tone data is decompressed into a high spatial resolution bytemap by unpacking the high resolution pixels across the edge, and i
Do Anh Hong
Oliff & Berridg,e PLC
Xerox Corporation
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