Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-05-21
2001-07-24
Rogers, Scott (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S451000, C358S451000
Reexamination Certificate
active
06266154
ABSTRACT:
FIELD OF INVENTION
This invention relates to a grayscale enhancement method and system including a unique routine which eliminates or reduces the mottling effect of present halftoning techniques.
BACKGROUND OF INVENTION
Shades of gray on computer printers are achieved by a process called halftoning. In the halftoning process, halftone cells are created each including a number of pixels. By making all the pixels white, a white spot is created and, conversely, by making all the pixels black, a black spot is created. By making only a small percentage of the pixels black in a cell, the spot, to the eye, appears light gray and conversely by making a large percentage of the pixels black in a cell, the spot appears dark gray. In general, the number of gray levels available is a function of the number of pixels in a halftone cell.
However, a given printer's capacity is a function of the number of pixels per inch and the size of the halftone cell. For example, if a cell includes 9 pixels, there are 10 gray levels possible while if the cell includes 256 pixels, there are 257 possible gray levels. Thus, the finer the halftone screen, the fewer number of pixels in each cell and therefore the fewer gray levels available. So, a 600 dpi printer at a screen frequency of 200 lines per inch (lpi) has 10 possible gray levels while the same printer at a screen frequency of 120 lpi has 26 possible gray levels. Therefore, to achieve more gray levels, screen frequency and hence image resolution suffers.
So, the goal has been to increase the printer's image resolution on 600 dpi printers and achieve more gray levels at the same screen frequency. That is, a 600 dpi printer at 141 lpi results in 19 gray levels but with super dot techniques can produce 145 gray levels at 141 Ipi.
Even with such advancements in technology and the use of screen angling and spot spacing variation techniques, however, a phenomenon known as mottling occurs which makes photographic and other images appear to have bad complexions. See, in general,
Real World Scanning and Halftones
, Blatner and Roth (1993, Peachpit Press).
Current processes for correcting the mottling effect include techniques that unfortunately add significant storage requirements to the printer system.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide a grayscale enhancement method and system which eliminates or reduces the mottling effect of present halftone techniques.
It is a further object of this invention to provide such a grayscale enhancement method and system which corrects the mottling artifact without adding to system storage requirements.
It is a further object of this invention to provide such a grayscale enhancement method and system which results in magazine quality printing using standard laser printers.
It is a further object of this invention to provide such a grayscale enhancement method and system which can be implemented in existing printer software and integrated with other text enhancement techniques to produce a total system for producing quality text, line art, and photo images.
It is a further object of this invention to provide such a grayscale enhancement method and system which does not require significant software modifications or increases in processing requirements for the printer controller.
It is a further object of this invention to provide such a grayscale enhancement method and system which does not add any significant cost to the printer controller.
This invention results from the realization that the mottling effect of current halftoning techniques can be corrected, not by techniques which add significant storage requirements to a printer's controller, but by replacing full size, widely spaced black pixels with closer spaced black pixels of a smaller size such that the total percentage of darkness is maintained but the spacing between the adjacent black pixels is reduced thereby eliminating or reducing the mottling effect of current halftoning techniques.
This invention features a grayscale enhancement method comprising the steps of analyzing the state of selected pixels surrounding a subject pixel in a bit map; determining the number of selected pixels including the subject pixel that are black; and printing, at a location corresponding to the location of the subject pixel in the bit map, a fractional pixel related in size to at least the computed number of pixels which are black.
The step of analyzing preferably includes generating a window which moves about the bit map. The window is typically nine by ten pixels in area. The selected surrounding pixels are usually located at a predetermined set of vectors with respect to the subject pixel within the window. The predetermined set of vectors then each have a length n, for example 3,2 pixels and each vector preferably extends to a different corner of the window.
A number, e.g. 4=m pixels are selected as the surrounding pixels and printing includes driving a printer modulator to print a pixel of a size approximately x/(m+1) where x is the number of black pixels present in the set including the m surrounding pixels and the subject pixel.
The grayscale enhancement method of this invention comprises analyzing the state of a plurality of pixels in a portion of a bit map; generating a number of fractional size pixels for each black pixel of the plurality; and printing the fractional size pixels. The plurality typically contains m pixels and each fractional size pixel has a size 1/m. The number of fractional size pixels is then m.
The grayscale enhancement system of this invention includes means for analyzing the state of selected pixels surrounding a subject pixel in a bit map; means for determining, from the selected pixels and the subject pixel, the number of black pixels; and means for printing, at a location corresponding to the location of the subject pixel in the bit map, a fractional pixel related in size to at least the computed number of pixels which are black. The means for analyzing includes means for generating a window which moves about the bit map. The window is preferably nine by ten pixels in area. The means for analyzing further includes means for selecting surrounding pixels that are located at a predetermined set of vectors with respect to the subject pixel within the window. The predetermined set of vectors each have a length n, e.g. 32 and each vector extends to a different corner of the window. Printing includes driving a printer modulator to print a pixel of a size approximately x/(m+1) where x is the number of black pixels present in the set including m surrounding pixels and the subject pixel m may equal 4.
The grayscale enhancement system of this invention includes means for analyzing the state of a plurality of pixels in a portion of a bit map; means for generating a number of fractional size pixels for each black pixel of the plurality; and means for printing the fractional size pixels. The plurality contains m pixels and each fractional size pixel has a size 1/m. The number of fractional size pixels is m.
REFERENCES:
patent: 5504462 (1996-04-01), Clanciosi et al.
patent: 5533150 (1996-07-01), Zulian
patent: 5659399 (1997-08-01), Lin et al.
patent: 5666470 (1997-09-01), Parker
patent: 5687297 (1997-11-01), Coonan et al.
patent: 6081625 (2000-06-01), Sakaue
patent: 0 528 365 A2 (1993-02-01), None
patent: 0 633 688 A2 (1995-01-01), None
patent: 0740 457 A1 (1996-10-01), None
patent: WO 89/08962 (1989-09-01), None
patent: WO 95/02938 (1995-01-01), None
Patent Cooperation Treaty, International Search Report, International Application No. PCT/US99/11344, mailed on Aug. 11, 1999, 6 pages.
Oak Technology, Inc.
Rogers Scott
Testa Hurwitz & Thibeault LLP
LandOfFree
Grayscale enhancement system and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Grayscale enhancement system and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Grayscale enhancement system and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2483228