Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1999-10-06
2003-01-21
Brier, Jeffery (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C358S003060, C358S003200, C358S003270
Reexamination Certificate
active
06509903
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to systems and methods for producing halftone images from digital representations of color images, the image to be recorded as latent or visible images by an output device such as image-setter, plate-setter or a digital printer.
GLOSSARY OF TERMS
Trapping—creating an overlap (trap/frame) between abutting colors to compensate for imperfections of the printing press.
Anti-aliasing—eliminating visibly jagged steps along angles or object edges, created by sharp tonal contrasts between adjacent color areas.
Screening—creating a pattern of dots to reproduce color or grayscale continuous-tone images.
Xerography—An electrostatic non-impact printing process in which heat fuses dry ink toner particles to electrically charged areas of the substrate, forming a permanent image.
BACKGROUND OF THE INVENTION
In the graphic arts industry, a half tone image, representing the image to be printed as a latent or a visible image, is produced from a digital representation of the image. This digital representation is produced in a workflow that includes two major stages.
In the first stage, performed using an image editing computer, such as a Macintosh, available from Apple Computer Inc. of Cupertino, Calif. and equipped with image-editing software, such as Adobe PhotoShop, available from Adobe Systems Inc. of San Jose, Calif., digital images to be recorded are created and edited by a graphic arts designer. This image editing usually includes one or more page-element specific operations, such as manipulating the colors of an image and preparing a page layout incorporating all the defined page elements in a Page Description Language (PDL).
In the second stage, a series of processes are applied to the input PDL file, resulting in a halftone image to be recorded by a digital front-end (DFE) application. The DFE may be connected to one or more output devices.
FIG. 1
schematically outlines a typical prior-art pre-press to press system, in which an analog picture is scanned (step
10
) using a scanner such as the Smart 342, commercially available from Scitex Corporation Ltd. of Herzlia, Israel. This produces a digital representation of the original. The digital file is then edited by the designer in step
12
, using software applications such as Adobe PhotoShop, and a page is constructed in step
14
, using software applications such as Adobe PageMaker, both available from Adobe Systems Inc. of San Jose, Calif., for color editing and page layout, respectively. The resulting digital representation of a page is converted to a standard file format, such as PostScript, PDF or other page description language.
The standard file is used as an input digital representation to a front-end system
16
, connected to an output device
18
that may be an image-setter, a plate-setter, a xerographic digital printer or any other known device for printing. The front-end system such as the Brisque, commercially available from Scitex, produces a half tone image from the input digital representation, after a series of operations, i.e., raster image processing, trapping, anti-aliasing and screening.
FIG. 2
schematically outlines a similar system, with the same basic flow, where the front-end system is connected to several output devices
20
in parallel.
In the prior art configurations of
FIGS. 1 and 2
, the decision of when and where in the process to perform the second stage operations such as trapping, anti-aliasing and screening is insignificant, Each of the second stage processes requires the page description file as input, as well as precise knowledge of the output device's characteristics and can be performed anywhere in time, between the page layout stage and the imaging or printing stage.
In one state of the art workflow used by Scitex, the digital page file is rasterized first, to create an intermediate file. The intermediate file goes through an automatic trapping application, such as Full Auto Frame available from Scitex, which automatically analyzes, decides and creates traps where desired, to produce a trapped intermediate file which is then screened. In this workflow, screening is performed in the front-end system, by applications such as Scitex Class Screen or Scitex Turbo Screen, operating on a digital file that has already been trapped.
In another state of the art workflow, trapping is done during rasterization, such as in the In-RIP Trapping application, available from Adobe Systems Inc. of San Jose, Calif. In this workflow, one can define trapping parameters prior to the RIP, to be executed during the RIP process.
In yet another workflow, the trapping functionality is found within the QuarkXpress application, available from Quark Inc. of Denver, Colo. and is performed before conversion of the digital image to a standard page description language file.
There are yet other ways to process the file provided to the front end in a standard file format. Most of them do not take into account the effect that any specific image processing operation might have on the outcome of subsequent image processing operations, in conjunction with a specific output device. For example, the trapping process often results in narrow color areas (trap areas) between specific color combinations of adjacent colors. These tap areas, when imaged by a specific output device, are very sensitive to the imaging capabilities of the output device, in terms of various parameters, including screen resolution, dot size, angle and shape, as well as the actual width of the trap. All of these parameters depend on the type of device that will produce the visible image.
The existing methods for pre-analyzing a file for possible imperfections in printing (resulting from the data of the file and the characteristics of the specific printing device), usually try to prevent those imperfections by modifying the digital data prior to printing, thereby possibly introducing artifacts into the file, enlarging its storage size and creating device-dependency which reduces the flexibility to produce the file on other types of devices, or with different output parameters (i.e. different size, resolution etc.) on the same device.
In general, image processing performed on an image file can produce different results on different output devices, depending on the characteristics of the output device. Thus, in the prior art, the parameters of the specific output device have been used as constraints to the image processing algorithms in order to achieve quality and predictability of output. On the other hand, processing that considers the parameters of a specific output device is less general and requires that the processing be performed separately for each output device.
European Patent Publication EP 0840500 A2 to Adobe Systems deals with the problem of output device dependency by suggesting a method for device independent trapping. According to EP 0840500 A2, the entire trapping algorithm is performed independent of the specific output device, leaving only the determination of the actual trap color to the final printing stage, This solution deals only with the appearance of the trap color and does not address other quality issues as described above.
SUMMARY OF THE INVENTION
The present invention provides a workflow for producing improved half tone images to be recorded as latent or visible images by an output device connected to a front-end system.
It is an object of the present invention to provide a workflow divided into two stages; the “preparation stage”, which is output device independent and results in a set of parameters, and the “production stage”, which involves the actual creation of the visible or latent image on a specific output device, using the parameters created by the preparation stage.
In one aspect, the present invention provides a method for enhancing the quality of a digital halftone image recorded on a substrate:
Initially, at least one color pair comprising two adjacent colors is identified in the digital image data, where there is a difference in color value between said two adjacent
Brier Jeffery
Creoscitex Corporation Ltd.
Cunningham G. F.
Eitan Pearl Latzer & Cohen-Zedek
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