Image Processing Reference
In-Depth Information
evaluated for color quality, and previewed
proofed on a monitor or on a workgroup
digital printer. After the proofs are approved for content, color, format, and quality the
job is submitted to the print queue. For high-volume offset jobs, digital documents are
imaged on the plate. For digital printing, the jobs are submitted to the press
=
—
in page
description language (PDL) format such as postscript (PS) or PDF
—
through the digital
front end (DFE) for further processing and printing. In the
finishing (post-press) stage,
the printed documents take on their
final form through cutting, folding, collating,
bundling, stapling, and
=
or packaging operations prior to shipment to customers. The
finishing work has a major impact on the
final product
s quality, which may be a topic,
'
folded
=
collated sheets, booklets nicely cut and bound, brochures, etc.
1.2.3 P
ROCESS
M
ANAGEMENT
Process management (the lower portion of Figure 1.1) tasks include scheduling
production, performing process-engineering functions, and organizing
file folders
and servers related to all jobs components and job archivals. Job noti
cation in the
event a new job arrives for production, job intervention, and customer communica-
tion handling is another key task executed in this step.
1.3 DIGITAL FRONT END
The printing stage normally contains: (a) a DFE (see Figure 1.2) and (b) a print
engine (see Figure 1.3). Unlike the workstation, where processing by the user may be
independent of the print engine, a DFE or a network of DFEs from multiple vendors
are used to convert the electronic
documents or job (through a series of
image processing applications such as trapping, segmentation, rasterization, color
management, image resolution enhancement, and antialiasing) to a form cyan (
master
''
''
C
),
magenta (
cally designed and optimized
for a particular digital printing system [3]. Multidimensional, industry standard
source pro
M
), yellow (
Y
), and black (
K
) that is speci
images to a device-independent form like
L*a*b* or standard Web offset printing (SWOP)
les are used to transform
RGB
files to device-independent
form. In some cases, the transformation may be direct between device-speci
CMYK
c forms
to printer-speci
c form. To this effect, the input document is transformed from its
PDL format such as PS or PDF, tiff, etc., to CMYK color separations to be printed by
the engine. For postscript images, this is done by
first utilizing an interpreter (e.g., PS
interpreter) to identify the commands found in the PDL. An imaging module then
generates a rasterized format of the PDL document at the correct resolution (e.g., 600
dpi). The above is usually referred to as RIP. During the RIP, color pro
les (e.g.,
International Color Consortium [ICC]) comprising of multidimensional
lookup
tables (LUTs) are applied that transform the color from
separations.
Some DFEs employ object-oriented rendering (OOR) algorithms intended to
enhance the color reproduction by utilizing custom profiles for specific image objects
such as a
RGB
to
CMYK
le for a blue sky background.
For OOR to be effective, segmentation algorithms must be utilized to identify the
objects of interest. Some DFEs also use trapping to mask registration errors; it is a
skin
pro
le for
eshtone or a
sky
pro
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