Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
2001-09-19
2004-09-21
Rogers, Scott (Department: 2626)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S003260, C358S518000, C358S540000, C382S167000, C382S205000, C382S199000, C382S275000
Reexamination Certificate
active
06795214
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of digital image processing in reproduction technology and pertains, more specifically, to a method of generating trapping contours at color edges in a print page. Such trapping contours serve for reducing the disturbances generated by misregistrations in the printing press, i.e. errors that arise when the colors are not printed on top of one another perfectly congruently but rather slightly shifted.
The artwork masters which are created for print pages in reproduction technology contain all the elements that are to be printed, including text, graphic objects, and images. In the case of electronically produced masters, these elements take the form of digital data. The data for an image are generated in that the image is scanned in a scanner by pixels and rows, each pixel is broken down into color components, and the color values of these components are digitized. The data for texts and graphic objects are generally generated directly in a computer by text processing and drawing programs. Depending on the output process that is to follow (i.e. output on a color printer or printing in a conventional printing press), the data for the page elements are generated in the color components red, green and blue (RGB) or in the colors of four-color printing, i.e. cyan, magenta, yellow and black (CMYK). The colors are printed on top of one another on the print medium (e.g. paper) in the color printer or the printing press.
Next, the digitized text, graphic objects, and images undergo diverse processing (e.g. color correction or modification in arrangement and shape, and final assembly into a print page) in a processing station in accordance with the specifications of a layout, while being visually monitored on a color monitor. The print page data are then converted into a data format which is suitable for output, for instance in the page description language PostScript, and stored. In this process, separate print page items of data, known as color separation data, are generated for each of the colors CMYK. The color separation data are recorded in high resolution on film material or directly on printing plates using a film or plate recorder. There also exist digital printing presses which work without plates. With these, the color separation data are transferred directly to the digital printing press and printed on the print medium there.
One problem that arises in printing technology is misregistration in the printing press, i.e. errors which occur when the colors are not overlaid perfectly congruently, but rather shifted relative to one another, in the printing units through which the paper continuously runs. These errors will now be demonstrated in a simple example wherein a red circle is printed on a black background. With reference to
FIG. 1
, subfigures
1
a
and
1
b
represent the color separations Y and M, the superimposition of which produces the red circle, and
FIG. 1
c
represents the color separation K of the black background from which the area of the circle is missing.
FIG. 2
represents the print result when the color separations Y, M and K are precisely superimposed in the printing press. The color separations Y and M completely fill the missing circle area in the color separation K.
FIG. 3
represents the print result given misregistration. In this example, the color separation K has been shifted up and to the right relative to separations Y and M, so that the separations Y and M no longer completely fill the missing circle in separation K, and an unprinted stripe
1
emerges. Since the unprinted stripe
1
is the color of the paper, which is typically white, it contrasts sharply with the red and black colors and is perceived as obtrusive. The shifting of the color separations also produces a stripe
2
wherein all three separations Y, M and K are superimposed on one another. Since, in this case, the brighter colors Y and M are printed on the dark color K, this stripe
2
does not disturb the print result. For purposes of illustration,
FIG. 3
represents a very large shift of the color separations. But the unprinted stripes that emerge given smaller shifts, such as occur in practice in printing operations, are also very obtrusive, and countermeasures must be taken to eliminate or reduce these errors.
One possibility for eliminating or reducing the above described disturbing effects caused by misregistration is to control the printing plate register or the paper feed in the printing press more precisely. But this is expensive and requires a large outlay, and it is not always possible to retrofit older printing presses with better control devices.
A second possibility consists in what is known as trapping in the preparing of the color separation data in the reproduction technique. Trapping is effected during the preparation of the color separation data. A trapping frame is generated in some color separations but not in others. The trapping of the correct color separations ensures that a sufficiently large overlap of the graphic objects in the color separations will still exist even given misregistrations in the printing press, and consequently obtrusive unprinted stripes cannot emerge. For which color separations a trapping frame must be created and for which not depends on the colors in the graphic objects relative to the colors in their immediate environment. As a general rule, the brighter colors are trapped vis-a-vis the darker colors. The outlines of the darker colors, which determine contour, are not changed, and the shapes of the graphic objects are thus subjectively maintained despite the overlapping of the color separations when they are printed on top of each other.
With reference to
FIG. 4
, there is shown a trapping frame
3
for the color separation Y from the example of
FIG. 1
; i.e., the circle is enlarged by the width w. When the circle in the separations Y and M is enlarged, but not the empty circular area in the separation K, then obtrusive stripes cannot emerge even when the color separations are shifted. The width w of the trapping frame
3
must be selected large enough to cover the maximum expected shift; i.e., the width is dependent upon the quality and age of the printing press that is used.
According to the prior art, the trapping frames are created by first analyzing which graphic objects are contained in a print page and where they adjoin one another. Depending on the type of objects and the colors on either side of a color boundary, it is then determined which of the objects will acquire a trapping frame and which color the trapping frame will take. The term graphic object refers to an area of arbitrary shape which is filled with color values in an arbitrary fashion. In the simplest case, the area is evenly filled with a constant color. But it can also contain a vignette, i.e. a continuous variation of the colors in a particular color gamut. But a graphic object can also contain scanned image data or a pattern of different color values. The type of color fill determines the type of graphic object, e.g. “uniformly colored area”, “vignette”, or “image”. The patent U.S. Pat. No. 5,113,249 teaches this kind of method for creating trapping frames according to the prior art. There, the type of graphic object is designated the “area type”, and depending on the “area types” on either side of a color boundary, it is decided whether or not to create a trapping frame, which of the two area types to widen with it, and which color the trapping frame should take.
In the methods according to the prior art, the types of graphic objects on the print page and the boundaries of the objects must be determined. If the print page is defined in an object-oriented page description language such as PostScript, this can by accomplished by analyzing the page description. That type of method is described in the patent U.S. Pat. No. 5,295,236. If the print page is not given in an object-oriented description but rather as a matrix of pixels, then the graphic objects and their boundarie
Funke Volkmar
Weinholz Peter
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Locher Ralph E.
Rogers Scott
Stemer Werner H.
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