Image Processing Reference
In-Depth Information
8 One-Dimensional,
Two-Dimensional,
and Spot-Color
Management and
Control Methods
8.1 INTRODUCTION
A key attribute of high-quality color printing is color consistency within a job, from
job-to-job, and from printer-to-printer. For example, a publisher might want to
print millions of copies of a book on dozens of print engines. One risk is that the
different print engines may produce copies that appear different. Print engine colors
drift. For high-quality consistent color rendition, the processes internal and external
to the print engines have to be controlled at regular print intervals. Pro
ling and
calibration are two important control functions normally implemented external to the
print engine, that is, in the digital front end (DFE). These functions involve the
printing, measuring, and processing of control patches for a particular paper and
halftone screen. They are normally executed on an
as needed
basis at a lower
''
''
frequency than the internal control functions.
The pro
ling and calibration of a conventional four-color (cyan, magenta,
yellow, and black) digital printer involves (1) generating a three-dimensional (3-D)
pro
ling lookup table (LUT) for mapping the device-independent L*a*b*orXYZ
color space to device-dependent CMYK color space based on measurement of color
patches, as described in Chapter 7, and (2) constructing device tone reproduction
curves (TRCs) that are one-dimensional (1-D) or two-dimensional (2-D) input CMYK
to output CMYK maps, both in device-speci
2-D CMYK maps are
used to account for device variability over time. Figure 8.1 shows a schematic of the
image-processing path with the destination pro
c space. The 1-D
=
le, CMYK to CMYK calibration map,
and a print engine with numerous details omitted for clarity. This chapter provides
detailed algorithms and methodology to generate 1-D
2-D calibration maps. We
show both model-based and (more sophisticated) control-based techniques. At the
end of the chapter, we extend the control-based methods to generate an accurate
spot-color recipe in device-speci
=
c space (CMYK) to render
fixed colors that may
be Pantone colors, customer logo colors, colors in a customer
'
s proprietary marked
patterns, or customer-de
ned colors in the form of an index color table.
431
Search WWH ::




Custom Search