Image analysis – Applications – Document or print quality inspection
Reexamination Certificate
1998-05-22
2001-06-19
Patel, Jay (Department: 2623)
Image analysis
Applications
Document or print quality inspection
C358S500000, C382S260000
Reexamination Certificate
active
06249592
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the color detection arts. It finds particular application in conjunction with neutral color detection in color copiers and/or scanners, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications where color detection is desired.
In color image processing, reproduction, recording and the like, a page of image data is read and typically a three-color, cyan-magenta-yellow (CMY), system is employed for rendering. Optionally, a fourth color, black (K), is included. Generally, combinations of the colors CMY are applied in relative proportions to produce the color portions of the image. Additionally, the CMY colors can be applied to produce a resultant black. However, the resultant black achieved by combining the CMY colors is not as high quality as that achieved with the true black (K). Chromatic noise, misregistration, and the like can degrade the quality of black images generated by a CMY resultant black application. Moreover, multiple CMY passes are relatively more time consuming compared to a K pass, and they increase the depletion of CMY inks and/or toners. Generally, these and other inherent constraints, limitations, and/or reproduction demands associated with color processing and/or printing make it desirable to limit CMY utilization where possible.
In the past, there have been developed techniques for determining if input pages are neutral in color (i.e. black and white, or monochromatic) to thereby reduce CMY utilization where it was not necessary. For example, in U.S. Pat. Nos. 5,287,204 and 5,282,026, incorporated herein by reference, such techniques are disclosed. However, both references achieve limited results. That is to say, the references are directed to detecting at the page level and determining if an input page is neutral in color. Generally with these techniques, each page as a whole is classified as color or neutral, which results in either the whole page undergoing color processing or none of the page undergoing color processing. As such, these approaches fail to address, for example, chromatic noise in a neutral region of an otherwise color page. Moreover, no provisions are made for high quality neutral detail, such as text, that may be located in a color page or region thereof.
The present invention contemplates a new and improved multi-resolution neutral color detection method and system which overcomes the above-referenced problems and others.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a method of neutral color detection for use in color copiers and scanners is provided. It includes reading an input page, detecting the page, and determining if the page is neutral in color. The page is then divided into a number of regions when the page is determined to be not neutral in color, each region is detected, and a determination is made if each region is neutral in color. Next, details outside regions determined to be neutral in color are detected, and it is determined if the details are neutral in color.
In accordance with a more limited aspect of the present invention, the page is detected by scanning a first averaging filter having a first block over the page, the regions are detected by scanning a second averaging filter having a second block over the regions, and the details are detected by scanning a third averaging filter having a third block over the details. The size of the third block is smaller than that of the first and second blocks.
In accordance with a more limited aspect of the present invention, the first block and the second block have sizes substantially the same.
In accordance with a more limited aspect of the present invention, during the detection of each region, averages obtained by the second averaging filter are ignored in determining if the region is neutral in color when the second block encompasses a boundary of the region.
In accordance with a more limited aspect of the present invention, during the detection of each region, averages obtained by the second averaging filter do not include pixels located outside the region when the second block encompasses a boundary of the region.
In accordance with a more limited aspect of the present invention, the detecting of the details and determining if the details are neutral in color further includes detecting edge pixels of the details. The third averaging filter is scanned over interior pixels of the details, and it is determined for each interior pixel if it is neutral in color based upon an average of pixels encompassed by the third block. For each edge pixel in turn, the third block is located such that the edge pixel is centered therein. A pixel having a relative intensity that is more extreme than an intensity of any other pixel located within the third block is chosen, and pixels located within the third block whose intensity varies by a degree greater than a predetermine threshold from the intensity of the chosen pixel are disregarded such that only a number of remaining pixels are left. It is determined that the edge pixel is not neutral in color when the number of remaining pixels that are not neutral in color is greater than a first predetermined number, and it is determined that the edge pixel is neutral in color when the number of remaining pixels that are neutral in color is greater than a second predetermined number. The determination is made that the edge pixel is unknown when a determination regarding the edge pixel has not otherwise been made.
In accordance with a more limited aspect of the present invention, edge pixels determined to be unknown are classified as not neutral in color.
In accordance with a more limited aspect of the present invention, edge pixels determined to be unknown are classified as one of not neutral in color when an immediate neighboring interior pixel determination is not neutral in color, and neutral in color when an immediate neighboring interior pixel determination is neutral in color.
In accordance with a more limited aspect of the present invention, the chosen pixel is a darkest pixel within the third block when the detail is dark on a light background, and the chosen pixel is a lightest pixel within the third block when the detail is light on a dark background.
A first advantage of the present invention is the high quality printing of gray image parts, and in particular black text.
Another advantage of the present invention is that ink/toner consumption and consequently ink/toner costs are reduced.
Another advantage of the present invention is that speed is increased by eliminating CMY printing passes where they are not otherwise appropriate.
Another advantage of the present invention is that its tunable thresholds permit a flexible approach adaptable to various applications.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.
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Banton Martin E.
Fan Zhigang
Zhang Yeqing
Fay Sharpe Fagan Minnich & McKee LLP
Patel Jay
Xerox Corporation
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