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ImageServer supports a wide range of image formats and color spaces. By default, the CMYK color space is used for output. This section describes how to setup a printer queue for an alternative RGB workflow and explains possible pitfalls.

We have received several customer requests for supporting an alternative workflow using RGB images and composite output without color matching. This is not possible using ImageServer with default color matching settings.

Such a workflow may be useful, e.g. for creating PDF files with unchanged composite images (RGB, CMKY, or Lab-based). The images must be tagged with an ICC profile and the output queue must not have any ICC profiles attached to make sure that no color matching occurs during output.

To change the default behavior of ImageServer for a specific queue the following commands must be performed:

cd /usr/local/helios
bin/prefvalue -k 'Printers/<printer queue>
/CompositeColorspace' -t str "None"

Change "printer queue" above to the name of the queue you want to change. The queue name has to be exactly the same name as displayed in the Printer Name field in the HELIOS Admin Printers configuration window.

To revert these setting to use again the ImageServer default behavior do the following:

cd /usr/local/helios
bin/prefvalue -k 'Printers/<printer queue>
/CompositeColorspace' -d

Important: Choose the queue you want to change carefully because all composite images (regardless whether they are RGB, CMYK or Lab) will be sent to the output device without any color matching! These settings do make sense for example on a HELIOS "Create PDF" queue because the Distiller is able to handle all composite color spaces.

The output result of such a modified queue may also depend on the used image type (e.g. EPS or TIFF) and on the application used. An application may change RGB image data while printing. Therefore only low-resolution images (layouts) should be used because these are CMYK based. We suggest to test the workflow carefully for such potential flaws prior to using these new settings in a production environment.

This section describes, how the RGB-to-Hexachrome® color space conversion workflow can be set up.

To enable Hexachrome® output on a queue, certain preferences for this specific queue must be set:

cd /usr/local/helios
bin/prefvalue -k 'Printers/<printer queue>/ProcessInks' -t
strlist "Cyan","Magenta","Yellow",
"Black","Orange","Green"

Additionally, the order of the specified colors must match the order in the used Hexachrome® profile. If the order in the profile is different, modify the above mentioned command line according to the order in the profile.

Note: Please note that an inaccurately set preference may lead to faulty results! Read more about the usage of "prefvalue" in the Base manual.

Allocate the Hexachrome® profile as printer profile to the specific queue you want to use. Do not allocate a proof profile!

To enforce a Hexachrome® color separation, the
"ForceHexachrome.eps" must be placed in each page of the document (see below).

If you are using PrintPreview, the spot colors "Green" and "Orange" must be defined in the HELIOS Admin Spot Color editor (see A 3.3 "The spot color editor"). This enables PrintPreview to create a correct composite preview.

All placed images have to be "tagged" with an ICC profile, or must be allocated a default profile per folder/volume.

The HELIOS CD-ROM includes a file named "ForceHexachrome.eps" in the sample-images folder. This file defines six process colors: Cyan, Magenta, Yellow, Black, Green and Orange and needs to be placed in the layout application to enforce the six-channel separation output for printing. The file does not contain printable data.

Some Hexachrome® profiles are not compatible with the ImageServer software. E.g., a Hexachrome® profile using the data color space "MCH6" is not supported by ImageServer. However, in order to still make use of the profile the data color space "6CLR" must be specified.

To do so, modify the profile in a data editor such as "HexEdit" (hexedit.sourceforge.net). Open the profile and replace in bytes 17 to 20 "MCH6" by "6CLR" (no quotes!).

ImageServer and PrintPreview cannot calculate a composite preview of a separated print job with spot colors if the application which has created the document does not send any process color information for the spot colors in the document.

For this purpose, PrintPreview has built-in color tables which recognize various spot color names, so process color information can be provided for the composite preview generation in PrintPreview. However, if a used spot color name does not match the exact entry in the built-in table, PrintPreview generates a composite preview which lacks the spot colors.

The spot color editor enables the user to define a preview color for a custom spot color name. This allows PrintPreview to include spot color objects in the composite preview.

In HELIOS Admin, open Spot Colors from the Settings menu.

Fig. A-5: The Spot Colors definition window

The Spot Colors definition window (Fig. A-5), which may already contain the names of some previously defined spot colors, opens. For the definition of a new spot color in the spot color editor, CMYK or Lab values are accepted.

In the Color Space section, select the appropriate color space and enter the values of your spot color. After that, specify a name for the defined spot color and confirm the settings by clicking the Save button.

The Revert button sets all entries back to default or, if you have only modified an entry, reverts to the latest saved version. After closing the window the new spot color appears in the list (Fig. A-5).

Fig. A-6 shows the ColorSync profile settings for an RGB monitor on Mac OS 9.

Fig. A-6: ColorSync profile for RGB

Note: On Mac OS X, go to System Preferences > Displays and select in the Color tab the display profile that suits your monitor.

Fig. A-7 shows the profile settings for a CMYK printer on Mac OS X. Both settings are used to represent accurate previews in the Spot Colors definition window.

On Mac OS X, the ColorSync utility is used to set printer profiles.

Fig. A-7: ColorSync profile for CMYK

Open Control Panels > ColorSync from the Apple menu and assign appropriate profiles from the pull-down menu to the output devices that you want to use.

These chosen profiles are displayed in the Spot Colors definition window. Fig. A-8 shows an example where the spot color "Gray" has been defined in the Lab color space. The color patch displays the accurate color according to the monitor profile. The CMYK values displayed below the color patch indicate how the Lab color is converted for printing.

Fig. A-8: Lab to RGB/CMYK

Important: Make sure to use the appropriate monitor and printer profiles, which can be created with ICC profiling tools. Wrong profiles, e.g. the default profiles used by Mac OS 9, or bad profiles, will lead to inaccurate results!

Fig. A-9 shows an example where the spot color "Gray" has been defined in the CMYK color space, according to the selected printer profile. The color patch displays the accurate color according to the printer and monitor profiles. The Lab values displayed below the color patch represent the CMYK color in the Lab color space.

Fig. A-9: CMYK to RGB/Lab

Since colors are best and most reliably represented in the Lab color space, it is sensible to enter the color in Lab values which have been determined by a spectrophotometer, e.g. "GretagMacbeth".

Note: To make profile changes in the ColorSync dialog valid, the ColorSync dialog and the Spot Colors definition window must be closed. The new ColorSync profiles will be used at reopening the Spot Colors definition window.


HELIOS ImageServer UB User manual

HELIOS ImageServer UB User manual