New useful tools for the color space

Color management II A topic that many
prepress departments and agencies, is the transformation of
CMYK in CMYK for various printing applications. The so-called DeviceLink profiles are used here.
 When automating a
Color management workflows within a PDF workflow environment with the
The aim of improving the quality of the output is to
which generate so-called DeviceLink profiles and
process. The DeviceLink profiles themselves are nothing new.
They are already mentioned in the first ICC profile format specification.
speech. But only now are programs and modules available with which
which DeviceLink profiles can also be generated and used in the PDF workflow with
additional benefits. It is therefore worth taking a closer look at these profiles.
to take a closer look.

DeviceLink profiles are defined as a transformation from a source
according to a target color space (usually from CMYK1 to CMYK2). This means that
They are ideally suited for converting data from, for example, "sheet-fed offset CMYK" to
"Digital proof CMYK" with integrated color rendering intent (rendering
Intent). For this reason, this profile class
in the image files, but - according to their function in the
workflow - only together with the Postscript or PDF files that
process images with embedded color information.

Loss of quality
From color space transformations carried out with DeviceLink profiles
This results in a higher quality of adaptation. It is based on the
richer functional possibilities compared to conventional
ICC transformations. This is because links from
ICC device profiles are created via the "detour" of a device-independent
profile link color space (PCS). The source profile used in
is in a device-dependent color space - such as RGB or CMYK - will be
is first converted to XYZ or L*a*b* and then converted back to
into a device-dependent color space, namely that of the target profile
(mostly CMYK).

Advantage of the conventional method: The profiles are flexible
linkable and interchangeable. Disadvantage: Especially with
CMYK-CMYK adjustments (ambiguous 4-3-4 channel transformation)
all separation settings are lost. Further blurring
result from the freedom of CMS programming that the ICC
which ultimately ensures maximum repeatability at all times.
quality (i.e. color accuracy) is counterproductive.

By linking DeviceLink profiles directly from the direct linking of
source and target profiles are generated (unique 4-channel
transformation), the desired properties are retained, even if the
z. e.g. the black tone value curve. These properties can even be
can be optimized, for example if a machine profile of a
Heatset web offset press adapted to coldset (newspaper printing)
and - which makes sense - significantly reduced the total amount of color
is to be used. Further useful application examples are listed in table
1 has been compiled. For each specific practical case, a
DeviceLink profile, but the result is optimal.
Especially in agencies that use proof files from the prepress plants.
and print shops in-house, the benefit justifies the
manageable effort.

Like device profiles, link profiles can also be applied to either all or
only selected document pages, which is useful for separations and
color quantity-related interventions proves to be helpful. Likewise, in
usually individual settings for graphics and fonts
intended.

Useful tools
Table 2 provides an overview of the available solutions. The
The GMG company pursues the philosophy of direct customization of
from the beginning and has been a pioneer for many years, other providers
have now followed suit. Whether as stand-alone software, plug-in or
module in the proof or color management solution - all of which are included in the
the link profile generation, the separation maintenance and the
control of the CMYK structure to the functional scope, not always also the
Limitation of the total amount of color in the print.

A common option is black point compensation (this sets the
black of the source image to the black of the output device in order to
dynamic range of the output color space) can be activated, the
to prevent color casts in the area of the gray axis. The left
The necessary analysis of the source and target profile is quasi
"CMYK preflight" can be used, from which some programs generate warnings.

There are differences in the manipulation options of the
separation curves (TRC) or point gain compensation as well as for the
Handling of link profiles in the workflow. The latter requires
server functionality that is either part of the solution or that is a
must supply an existing or additional product. Here
the range extends from the profile server to a few workflow and
proofing systems through to dedicated PDF color servers (see box).
With the help of the link profiles, this carries out color space and
PDF-PDF transformations.

DeviceLink profiles as a supplement
Thanks to DeviceLink profiling, the abstract and complex
Colormanagement adds a piece of practical relevance. For the free
Linkability of RGB input profiles with CMYK output profiles is suitable
The ICC transformation is still underway, whereas the
DeviceLink profiles for CMYK-CMYK transformations.

Dieter Kleeberg

PDF color server
To take advantage of the benefits of a DeviceLink-based color space transformation
PDF color servers are available. These dedicated servers have
the task of creating an automated workflow
Apply color space transformations to PDF files. In defined
hotfolder actions, the selected input and output profiles are
and rendering intents linked via a profile link color space
(RGB-CMYK) or if required (CMYK-CMYK) directly to DeviceLink profiles
processed. Through targeted editing of the output profile in
a server dialog mask, the desired
Separation adjustments and color quantity limitations effective.

During the color space transformation, the PDF color server (which acts as a
Acrobat plug-in or workflow tool) that can be implemented in the
PDF workflow, e.g. the Acrobat Distiller. The
The result is a new printing process that is optimized for the respective
Color reproduction and ink quantity optimized PDF file.
PDF color servers are offered by the providers listed in the table "--".
The company Alwan Color Expertise takes a slightly different approach with
its product CMYK Optimizer. The software calculates
DeviceLink profiles dynamically based on source and target profiles
taking into account an analysis of the respective print data. Through
The preceding analysis of the print data is always
DeviceLink profile created. (dk/jf)

Further links: The German-speaking manufacturers and the reseller Impressed offer neutral or product-related information on the topic.
Also recommended:
www.devicelink-colormanagement.com; discussion forum requiring registration (still under construction)
www.impressed.de/devicelink.html; online test server for DeviceLink profiles.