Image analysis – Image enhancement or restoration – Edge or contour enhancement
Reexamination Certificate
1999-06-03
2003-02-25
Lee, Thomas D. (Department: 2724)
Image analysis
Image enhancement or restoration
Edge or contour enhancement
C382S254000, C358S448000
Reexamination Certificate
active
06526180
ABSTRACT:
FIELD OF INVENTION
A pixel image enhancement system for higher resolution black and white and color images including alphanumeric characters and graphic video game designs displayed on such devices such as computer monitors, printers, facsimile machines, television screens, video game displays, and the like.
BACKGROUND OF INVENTION
A need for higher resolution image production is well documented in the art. A close inspection of letters and graphic images on a computer screen or a hard copy print out reveal jagged lines causing an unsightly rough appearance of displayed and printed images.
One method of ameliorating this problem, disclosed in U.S. Pat. No. 4,437,122 to the Xerox Corporation involves isolating a center pixel, matching the 3 by 3 pixel pattern surrounding and including the center pixel with a table of “standard pixel formats”, and then subdividing the center pixel area into enhanced “subpixels”.
Another method utilizes pattern matching templates operating on a window with a central bit. See U.S. Pat. No. 4,847,641 assigned to the Hewlett Packard Corporation.
One disadvantage in the prior art is the use of “standard pixel formats” and templates. When the selected pixel and the surrounding pixels to be analyzed are few in number, for example a 3 by 3 pixel matrix, and when the pixels are only bi-valued (black or white), the total number of possible input patterns is small. A 3 by 3 matrix of input pixels, each either black or white, has a total of only 512 possible patterns which, in contemporary hardware or software can easily be handled by placing 512 hand selected “answers” (“templates” or “standard pixel formats”) into a look-up table. The analysis of only a 3 by 3 pixel matrix is very error prone, however, since the pattern analyzed can be indicative of a line angled at 45° or the beginning of a curve. Analyzing a larger subset of the input pixel matrix requires the formation of a very large unwieldy number of standard pixel formats or templates.
The templates disclosed in the Hewlett Packard patent are similar to input windows except for having a third pixel state in addition to black or white. The third state is called a “don't care” condition. This allows each template to represent many possible inputs specifically two to the power of the number of “don't care” conditions in a given template, thus greatly reducing the number of templates required. Such trivalued templates, however, are still very limited. For example, if one tiny feature is to be allowed two different ways, two completely separate templates are required.
Although it may be fairly straight forward to straighten out a jagged 45° line according to this prior methodology, it is nearly impossible to use standard pixel formats or templates to account for the numerous possible permutations of angled lines, curves, and other features inherent in the display of alpha numeric characters and graphical displays. In addition, the prior art methodologies are generally constrained to bi-valued input bitmaps.
Another type of system involves the use of “anti-aliasing” filters which are linear. Anti-aliasing filters do not make inferences based on real world properties of edges such as slope continuity. Anti-aliasing filters remove spurious a high frequency information which is an artifact of the quantization process but they do not replace the spurious high frequency information with inferred hypothetical high frequency information.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide an improved pixel image enhancement system and methodology.
It is a further object of this invention to provide such a pixel image enhancement system and methodology which is not constrained to templates or standard pixel formats.
It is a further object of this invention to provide such a pixel image enhancement system and methodology which is not constrained by use of a center pixel, a center bit, or a small 3 by 3 input pixel pattern.
It is a further object of this invention to provide such a pixel image enhancement system and methodology which eliminates the requirement that the input pixels be bi-valued.
It is a further object of this invention to provide such a pixel image enhancement system and methodology which is able to handle any input pixel pattern and which enhances color images.
It is a further object of this invention to provide such a pixel image enhancement system and methodology which is implemented in hardware instead of software thereby decreasing the processing time.
It is a further object of this invention to provide such a pixel image enhancement system and methodology which can be used in conjunction with any type of output display device: CRT's, LCD displays, printers, facsimile machines, television, and which is easily housed within a chip which can be located in the output device.
It is a further object of this invention to provide such a pixel image enhancement system and methodology which employs an inferential algorithm for image outline detection.
It is a further object of this invention to provide such a pixel image enhancement system and methodology which utilizes a digital modulator, in some applications, for precise pixel positioning.
It is a further object of this invention to provide such a pixel image enhancement system and methodology which lowers the video subsystem cost.
It is a further object of this invention to provide such a pixel image enhancement system and methodology which lowers memory and processing requirements.
This invention results from the realization that a high resolution pixel image enhancement system can be accomplished, not by analyzing a central pixel of a small matrix of input pixels using templates or tables of standard pixel formats, but by detecting elemental edges between adjacent input pixels, generating an edge map, and using Boolean equations implemented in hardware to produce a segment of an inferred edge, within an output cell area, from the edge map resulting in higher resolution and accuracy than the inputted pixel map would otherwise allow. The result is a system which enhances color as well as black and white alphanumeric and graphic images and which can be used in conjunction with any type of display device: printers, CRTs, LCD displays, projection displays, television, facsimile machines and the like at a much lower cost. An unwieldy number of patterns or templates need not be designed and the system can be implemented on a chip which is placed in the output device or elsewhere for very high resolution.
This invention features a pixel image enhancement system and method. The system includes means, responsive to an input pixel map, for detecting edges between adjacent input pixels of the map. The edge may be defined by two adjacent pixels of different color. There are means for analyzing a set of pixels surrounding an output cell area partially overlapping a plurality of pixels including means for generating a case number characterizing the inferred edge based on the set of pixels surrounding the output cell. There are also means, responsive in the case number, for producing a display signal which drives an output device to display, to the best of its ability, the inferred edge.
In the preferred embodiment, the input pixel bit map is 640×480 pixels and the output device has a resolution of 800×600 pixels. The display signal is output for each pixel of the output device in the typical implementation. The system also features means for detecting an edge between adjacent pixels by identifying a difference of color between the adjacent input pixels. The means for generating a case number preferably includes a set of logic operations implementing Boolean equations defining the case number as a function of the set of pixels surrounding the detected edge. In a preferred embodiment, an edge map is generated which contains the detected edge.
This invention also features a pixel image enhancement system comprising means for creating an output cell which partially overlaps a plurality of adjacent input pixels, m
Lee Thomas D.
Oak Technology, Inc.
Testa Hurwitz & Thibeault LLP
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