Profiling is mandatory

Color management concerns everyone. Only by adjusting the color space with profiles can colors be reproduced as accurately as possible.
produced without a workflow supported by color management
but the majority of print jobs will certainly be printed at the latest when
no longer if the customer/client has high quality standards.
customer of the printed products is available. The consistent
ICC or ISO 12647 standardization is now an indispensable tool for
Part of production in the agency, prepress and print. But as soon as
you start with the topic of color management, you come to certain
Basics and English technical terms [in the text in square brackets]
which are presented below.

Color vision
Color vision in the printing industry is subject to defined
Conditions. For example, the most similar color temperature of the white light of
Monitors, proof lights and press viewing consoles 5000 Kelvin
the viewing must be glare-free and in a neutral gray color.
environment. Monitors should therefore not be placed by the window, and
There must be no other monitors, windows or screens on the screen.
Mirror luminaires. Proof luminaires and viewing panels must have a
Angle ratio between luminaire/desk and desk/eye from 0° to 45° for
a desk inclination of 0° to 22.5°. Visual
Color comparisons are based on a field of view of only 2°.

Since image capture and playback systems use different technologies
must represent both the types and sizes of their color spaces and their
also the ratios of the displayable color tones to each other
be characterized. This is done in the form of so-called
Device profiles that comply with the specification of the International Color
Consortium (ICC, www.color.org). The current
Specification is 4.1.

Color spaces
All visually detectable colors can be combined in one color space.
represent. The International Commission on Illumination (CIE) has developed
developed several color space models, of which CIE(1931) and
CIELAB(1976) are established in the printing industry. From the point of view of the
Color Management are "device-independent color spaces".
CIE(1931) describes the blue, green and red sensitivity of the
retinal receptors in the form of the three standard valences XYZ or
standard color value components xyY (known as "shoe sole"), which in turn determine the
mathematical basis for the description of color stimulus processing in the
brain in CIELAB(1976). Here the coordinates L* stand for the
brightness (gray axis), a* for the red-green chrominance and b* for the
Yellow-blue chrominance. This color space model allows,
To describe differences in color in a sensitively equal distance,
expressed in the so-called Delta-E values (DE).

In contrast, in "device-dependent color spaces" (DeviceRGB, DeviceCMYK
etc.) technically based color values represent the coordinates. RGB stands for
the color channels of a scanner, the sensors of a digital camera or
the phosphors or liquid crystals of a monitor. CMYK
describes the four process printing colors cyan, magenta, yellow and key
(black) for proof printers and printing machines. Naturally
color spaces with spot colors can also be defined - for example
Pantone Hexachrome CMYOGK (with O for Orange and G for Green).

Color Management adjusts color spaces
One of the challenges of color management is the
Adaptation of device color spaces of different sizes equal or
of different types, such as scanner RGB to monitor RGB, camera RGB to
Print-CMYK or Print-CMYK on Proof-CMYK. Such
Color space transformations are always carried out via a three-channel
device-independent color space, usually CIELAB. The
The necessary color calculator [Color Matching Module or CMM] is available in the Color
Management Framework interface of the operating system. In
In practice, the CMMs called ACE (from
Adobe), ColorSync
(Apple) and LogoSync (GretagMacbeth). Since the algorithms are not
are prescribed in detail, a specific CMM is always required for the
overall process.

The color space adjustment [gamut mapping], in which the respective
device profiles can be converted into each other, after
different color rendering intentions [Rendering Intents].
In the case of strong compression, such as a large scanner color space
to a small proof or print color space, is perceived as a small color space.
[perceptual/photographic]. With approximately the same size
color spaces - the color space range [gamut] in the proof should nevertheless correspond to the
completely cover the gamut of the printing press - the colorimetric
method [colorimetric], whereby a distinction is made between "absolute" (proof with
paper white simulation) and "relative" (proof on production paper)
is distinguished. The saturation-preserving method [Saturation]
does not play a role in printing.

In order to keep color information losses as low as possible and thus
to preserve the cross-media capability of the image data, images (and
graphics) are always edited in RGB mode, under
Application of so-called working color spaces. In terms of gamut, these are
and sensory uniformity of optimized profiles that
additionally in an image file with an embedded scanner profile
are included; the image is then in the RGB of the working color space
before. As with the CMM selection, it is advisable to specify a
specific working color space, such as Adobe RGB or eciRGB.
ISO standard is in preparation. The too small sRGB is
professional standards.

Profiles
Profiles are files that, like a fingerprint, identify the
Color rendering properties of a device, workflow section or
color space. They are stored in a data format similar to TIFF.
structure: The header of the format contains
all creation, type and white point information, the tag entries
include characterization tables, which are created with the help of
The color rendition can be corrected as far as possible with the help of target/actual differences.

Profiles are created for the different color space and device types.
created. Input RGB profiles are created by offsetting the
Actual values of a scan or digital camera image from a special
Test image [Target] with the corresponding target values. All other
Profile types require suitable data for recording the actual values.
Colorimetry. Display RGB profiles require a monitor colorimeter,
which measures color patches passing through one after the other. Output profiles (CMYK,
spot colors) can be achieved by measuring printed targets with
with a spectrophotometer. But be careful: Profiles have in
in practice is only valid if the production and
creation conditions are identical. Each changed condition
requires the modification or renewal of the profile.

The number of measured values within a profile or from several profiles
measurements, e.g. via a printed test edition for a
average profile, are decisive for the profile quality. For
output profiles is the ECI-2002 target from the Altona Test Suite
(www.eci.org) recommended using the Ifra test form for newspaper printing.
(www.ifra.com). Prefabricated average device profiles [Generic
Profiles] are too imprecise and should at least be modified.
Of course, this does not apply to the standard profiles that are included in the
process standard offset printing or ISO 12647-2 for the definition of
of the five paper classes and a color matching criterion for
digital proofs. Nor is the Ifra standard profile
to touch.

The performance of a profile also depends on the
supported ICC specification. Version 4.1 formulates the
rendering intents more precisely and requires data completeness, which is
White point calculation, paper white simulation and gray axis stability
under a measured intensity (lux value) of the illuminating illuminant
improvements and for profile and color identification
ensures distinctiveness. Further improvements concern the
Structure of monochrome profiles and profile-external tables
[look-up tables] as well as the handling of spot colors in multi-channel
profiles. Special colors in CIEXYZ or
CIELAB coordinates and their place in the print sequence
can be defined. The input, display and output profiles are available for
different sections of a workflow and must be analyzed in the context of
color space transformations are linked with each other, i.e. using
of a suitable rendering intent. Basically
the device color space to be mapped represents the source [Source
Profiles] and the color space of the device currently in operation the target
[Destination Profile]. The most common profile application scenarios are
Image processing under soft proof conditions, the location-independent
Softproof (Internet-based remote proof) and the digital proof, which
only with the successful verification of the color deviation tolerances in the
Ugra/ Fogra media wedge printed with the color accuracy status
can be achieved. Even print run proofs that are authentically screened are
already possible in true-color quality.

Color management via color server
Since a profile link is always established via a neutral three-channel
Profile Composite Color Space (PCS), i.e. CIELAB or CIEXYZ,
can be used for four-channel CMYK-to-CMYK transformations, e.g. with the
Change of paper classes from ISO coated to ISO uncoated
(uncoated), important separation setting for achromatic build-up (UCR,
GCR) or the mixing ratio of the color channels (CM, MY, CY) is lost
go. This problem was the starting point for the programming of
customized separation-preserving connection profiles
[DeviceLink profiles]. This technology is implemented in
Server applications with which DeviceLinks are prefabricated,
can be edited or redefined and which, in addition to
image data formats as well as PDF as input and output formats.
Conformity with the PDF document format qualifies these servers
also a tool that can even be used independently of
Separation settings reduce the total amount of color in a print job
without compromising the color reproduction quality. The
server to profiles, working color spaces and rendering intents via the
Acrobat Distiller.
Color management is therefore a bundle of technologies that can be
Awareness of the printing industry largely established as necessary
have. In the interest of avoiding operating errors and further
standardization, perfection is moving towards automation.
DeviceLink PDF color servers are the most recent example of this.

Dieter Kleeberg