Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-12-22
2001-08-14
Rogers, Scott (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S534000, C382S257000, C382S275000
Reexamination Certificate
active
06275304
ABSTRACT:
The present invention relates to the varying of colors and shape in the reproduction of various image features. Particularly, the present invention describes a method for varying the color of colored small image features, based on the size, shape, orientation or color thereof, to enhance appearance with minimal impact, or a preferential impact, on perceived color.
BACKGROUND OF THE INVENTION
Document printing in the home and in the office has evolved to incorporate color into a large number of documents. The use of color in documents has created problems in the area of printing color text, that extends to other small features in the document images. The readability of colored text is strongly influenced by the choice of color, not only due to the visual contrast between text and background, but also due to the printing process incorporating a finite set of colorants at a small number of defined local density levels.
Color in documents is the result of a combination of a limited set of colorants over a small area, in amounts selected to integrate to a desired color response. This is accomplished in many printing devices by reproducing separations of the image, where each separation provides varying amounts of a single primary colorant. When combined together with other separations, the result is a full color image.
For color images, a plurality of color separations are combined. Each color separation corresponds to a single colorant, and may be defined by a number of gray levels in excess of the capability of the printer. In such cases, each of the color separations is reduced from the input number of levels to the smaller output number of levels reproducible by the printer. The multiple color separations are combined together at printing to yield the final color print. Commonly, color documents are formed using cyan, magenta and yellow colorants or cyan, magenta, yellow and black colorants. A larger number, or alternative colorants may also be used. A color image may also be represented as sets of image planes representing quantities other than colorants. For instance, the color planes could represent parameters within a representation of color, such as L*, a* and, b* which describe lightness and two aspects of chromaticity, respectively.
In printing documents, the desired gray level over an area is commonly achieved by halftoning, where image gray level variation is represented by placing greater or lesser numbers of ON pixels in a discrete area of the image. In one halftoning method, known as dithering or screening, over a given area having a number of gray separation pixels therein, a value representing the gray level of each separation pixel of an array of gray separation pixels within the area is compared to one of a set of preselected thresholds as taught, for example, in U.S. Pat. No. 4,149,194 to Holladay. For an area where the image is gray, some of the thresholds within the dither matrix will be exceeded, i.e., the image value at that specific location is larger than the value stored in the dither matrix for that same location, while others are not. In the binary case, the image pixels or cell elements for which the thresholds are exceeded might be printed as a maximum colorant value, while the remaining separation pixels are allowed to remain white, dependent on the actual physical quantity described by the data. The described halftoning method produces an output pattern that is periodic or quasi-periodic in the spatial coordinates.
Halftoning creates problems in color document reproduction where color text and other small image features are used. One constant trade-off in color printing is between spatial resolution and color resolution. In order to reproduce a given color accurately, a comparatively large halftone cell has to be used. Large halftone cells allow more gray levels of each color, and therefore, more colors. However, the effect of this large cell is that small details can no longer be accurately rendered. The large halftone cell structure becomes visible to the eye. An impact of this phenomenon is that small colored text objects become illegible. If on the other hand, a comparably small halftone cell is chosen, the color of graphics and images is no longer accurately represented. However, if the halftones cells used to create the color are changed to smaller cells, the choice of colors becomes smaller as well, making it unlikely that the correct color can be obtained.
The problem of small color text reproduction extends to many other small features, including for example, structures in maps and other detailed illustrations, particular when such structures are in color. One notable example is the representation of a certain type of road on a map as a solid, thin colored line. If the road is improperly halftoned, the road may appear “dashed” and the original image intent is lost.
All of the references cited herein are incorporated by reference for their teachings.
SUMMARY OF THE INVENTION
In accordance with the invention, a processing system for preparing a plural separation document image for printing includes small feature enhancement of the image, preventing halftoning damage thereto. The process included detecting selected attributes in the document image, and in a detected selected attribute region, setting output image signals corresponding to said small feature region to ON, in at least one of said at least two separations. The process works particularly well for small text protection.
In accordance with one aspect of the invention, selected attributes including small features such as text may be identified by information from a page description language description of the document.
In accordance with another aspect of the present invention, selected attributes or small image features may be identified by a combination of one or more of size, shape, color, and intensity attributes.
In accordance with yet another aspect of the invention, small image features may also be identified by creating a mask identifying small feature areas of the image. By successively using erosion and dilation filters selected for detection of a size, shape, orientation, color or intensity to identify small features in the image, a mask identifying small text areas is created, and used for selecting areas of the image for halftone damage protection based on the mask.
The present invention describes a process to address the size/color choice dichotomy without the need to switch between halftone cells. This is achieved by dynamically varying the color transform as a function of the selected attributes of the image elements. In this way, small text, small graphics and lines can be subjected to a different color transform than large text, graphics or pictures. The main feature of the proposed method is the color enhancement of individual elements based on identification of their feature size, shape, and/or orientation. In one embodiment, the method enhances the color of small page elements by increasing their printability through luminance and chrominance changes. Large objects are not modified and maintain their original color. In this way, the method automatically changes the compromise between color accuracy and readability in an adaptive manner.
Any size, shape, intensity, orientation-based feature may be found through combinations of erosions and dilations. For instance, it may be desirable to identify only serifs and thin points of a stressed font (selected shapes) for modification. Alternatively, particular structures within an image, such as map symbols may be identified by shape for subsequent modification. Once identified, a mask is constructed for those structures, and pixels within and about that mask may be modified for to protect the feature by changing the color transform.
REFERENCES:
patent: 4149194 (1979-04-01), Holladay
patent: 5048109 (1991-09-01), Bloomberg et al.
patent: 5065437 (1991-11-01), Bloomberg
patent: 5201011 (1993-04-01), Bloomberg et al.
patent: 5204918 (1993-04-01), Hirosawa
patent: 5519109 (1996-05-01), Klassen
patent: 5655061 (1997-08-01)
Eschbach Reiner
Loce Robert P.
Costello Mark
Rogers Scott
Xerox Corporation
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