HP CMYK Plus
Use
HP CMYK Plus
User Guide
© 2004 Copyright Hewlett-Packard
Development Company, L.P.
Reproduction, adaptation or translation
without prior written permission is
prohibited, except as allowed under the
copyright laws.
The information contained herein is subject
to change without notice.
The only warranties for HP products and
services are set forth in the express
warranty statements accompanying such
products and services. Nothing herein
should be construed as constituting an
additional warranty. HP shall not be liable
for technical or editorial errors or omissions
contained herein.
PostScript® is a trademark of Adobe
Systems.
Part Number: Q7433-90909
Edition 2, 11/2004
Table of contents
1 Overview of HP CMYK Plus
2 Benefits of HP CMYK Plus
3 How HP CMYK Plus works
4 How to use HP CMYK Plus
iii
iv
1 Overview of HP CMYK Plus
HP CMYK Plus is a proprietary Hewlett Packard color management technology that allows you, with
just a few clicks, to take full advantage of HP Color 9850mfp full-gamut capabilities when printing
CMYK (cyan, magenta, yellow, and black) files. HP CMYK Plus supports intelligent color mapping
from standard CMYK file colors to more saturated vivid colors, leaving hue, skin tones, and grays,
and preserving original K-channel (black-channel) characteristics. This includes improvements in
contrast because of the higher dynamic range of the HP Color 9850mfp.
1
2
3
4
Black-only text and objects are printed using only black ink.
Skin tones are preserved.
Hues are preserved.
Colorfulness is boosted. HP CMYK Plus has similar colorfulness as the native color space, and at the
correct hue.
1
Until now, only three options have been available when working with CMYK files:
■ Simulate a well-defined press like SWOP (Specification for Web Offset Publications). Colors are
correct, but since these standards are designed for a wide range of printers, the colors are dull
when compared to the full capabilities of the HP Color 9850mfp printer.
■ Print in the native color space of the printer. This makes colors very saturated, but incorrect.
■ Open the file and edit colors to improve the appearance of the overall image. This is time-
consuming and expensive.
The HP Color 9850mfp provides a fourth option:
■ HP CMYK Plus re-renders press CMYK data, allowing direct CMYK-to-CMYK (4-to-4) mapping.
This method maintains press hues and K-channel, adapts lightness range, increases
colorfulness, and scales chroma in a non-linear fashion from press to output digital device to take
advantage of the full-color gamut.
HP CMYK Plus is not a rendering intent, but is implemented as an ICC device link profile.
NOTE HP CMYK Plus works with untagged (unknown) CMYK data prepared for a variety of
offset press standards. However, if you print a document with embedded profiles, HP CMYK
Plus will ignore the profiles and link the device to the CMYK color data. This is done to
incorporate the HP CMYK Plus effect during printing without the need to modify the document
file.
NOTE HP CMYK Plus works only on CMYK workflows, so it does not work on the PCL driver.
2 1 Overview of HP CMYK Plus
2 Benefits of HP CMYK Plus
Using HP CMYK Plus, creative professionals can produce impressive portfolio prints and
presentations using final CMYK files without clipped colors. Printers with HP CMYK Plus produce
outstanding output with rich and vibrant colors that is perceptually consistent with press-printed
documents in hue and lightness relationships. The output color looks just like offset four-color
printing, only better. HP CMYK Plus is the ideal complement for digital devices with wider gamut than
traditional offset.
Print service providers can produce output from standard CMYK files (prepared for offset) that take
full advantage of the gamut of the device at the first attempt, without manual intervention. This output
is perceptibly consistent with offset output and the original RGB file.
3
4 2 Benefits of HP CMYK Plus
3 How HP CMYK Plus works
When a digital printer receives a CMYK image without an attached color profile or other information,
it typically assumes that the CMYK values are to be interpreted directly using its own colorants.
HP CMYK Plus, on the other hand, takes into account the fact that most CMYK content is generated
for offset presses, and applies a different approach to rendering untagged CMYK data on a particular
digital printer.
The HP CMYK Plus re-rendering process works as follows:
1 It first ensures that the black (K) channel is preserved so that a given K value in the source data
is always replaced by the same black value in the destination (except for some rounding
differences).
Any source colors defined using K only (such as text, lines, or drop shadows) are also kept as K
only in the destination.
2 The color appearance of the untagged source CMYK data is interpreted by applying a press ICC
profile. The result at this stage would yield colors with the appearance of the source CMYK
printed on a conventional offset press.
3 Since the dynamic ranges of digital printers often differ from those of conventional presses, the
dynamic range of the initial color values is transformed (by either compression or expansion) to
fit that of the destination digital printer.
4 The shapes of digital printer color gamuts also differ from those of conventional presses in terms
of the levels of colorfulness that they can achieve at different hues and lightness levels. To make
better use of the color gamut of a digital printer, the levels of colorfulness are also transformed.
This results in more colorful digital prints than those obtained from an offset press, since the
gamut of the digital printer is larger. This is done without distorting the appearance of neutral
colors or familiar colors like skin tones. Throughout this re-rendering process, the hue of the
source color remains unchanged, since this is the color attribute that can be most objectionable if
changed in color reproduction. Keeping the hue as it would be on a press also means that
HP CMYK Plus output is still consistent with press appearance.
5 Destination CMY values are computed from the destination colors obtained above. The K
amount is determined from the results of the first step and by using the ICC profile of the
destination printer.
6 The resulting CMYK values are rendered on the destination printer.
The effect of HP CMYK Plus is illustrated in the figure below, where a CMYK image is shown after
being processed using different workflows on the HP Color 9850mfp with semi-glossy proofing paper.
5
Figure on left:
Native: Very saturated but incorrect.
Note greenish wall at 1.
Figure in center:
SWOP: Correct, but colors are dull.
Note the more saturated yellows at 2
and the greenish lawn at 3.
Figure on right:
HP CMYK Plus: Correct, and colors
are more saturated. Note the more
saturated yellows at 2 and the greenish
lawn at 3.
NOTE Due to the nature of the HP CMYK Plus technology, it is difficult to do these
differences justice with any single hardcopy process. Prior to printing, prepare an electronic
(PDF) copy of the document and view the file on a reasonably well-calibrated monitor.
6 3 How HP CMYK Plus works
1
2
3
4
5
6
Brightness
Colorfulness
SWOP gamut boundary
Grays (core)
HP Color 9850mfp gamut boundary
Limits of the expansion to avoid color clipping
This figure represents a slice of the color space where the source (SWOP or similar), and the
destination gamuts are represented. Source gamut is expanded to the orange limit in a non-linear
fashion to avoid artifacts. To keep neutrals, the core central part is not touched. Skin tones also
remain untouched.
7
In this representative figure, a slice of the color space top view and the printing options with the
HP Color 9850mfp are shown:
1 A proofing print rotates the color gamut (press inks are different than dry electro-photographic
inks), and tries to match the press gamut (SWOP) colors.
2 HP CMYK Plus also expands the colors in a non-linear fashion to take advantage of most of the
HP Color 9850mfp gamut, producing more vivid colors and improved contrast. Skin tones and
neutrals are left untouched.
3 Native colors print. This will leave wrong hue locations of the CMYK colorants.
8 3 How HP CMYK Plus works
4 How to use HP CMYK Plus
NOTE HP CMYK Plus technology is available in the PostScript® driver.
In the printer driver, click Properties. The Printing Preferences menu, comparable to the menu
below, appears:
In the window, click ColorWise, and the following window opens:
9
Click Expert Color, and the following window opens:
In this window, use the pull-down CMYK Simulation Profile menu to select HP CMYK Plus.
Click OK.
10 4 How to use HP CMYK Plus
You can use HP CMYK Plus with any of the output profiles in the device. The first time that you
select a new profile, the controller calculates the CMYK-CMYK device link and applies it. This could
impact ripping performance by few seconds only the first time that it is used.
You can also apply HP CMYK Plus to any profiles that have already been created.
NOTE Command Workstation and ColorWise Pro Tools use a comparable interface.
11
12 4 How to use HP CMYK Plus
© 2004 Hewlett-Packard Development Company, L.P.
*Q7433-90909*
*Q7433-90909*
www.hp.com
EFI part number:
Q7433-90909
Loading...