Spot Colors and Multicolor ICC Profiles

Generally, spot colors do not follow the restrictions (limited gamut) of the printing process simulated in the proof. Thus, the full gamut of the proof printer can be used when printing spots. The color management process undergone by process colors is generally not applicable to spot colors.

Spot color channels are generally defined in spot color sets in the GMG ColorProof database. If spot color sets are used, a further color management of spot colors is not required. If an image is opened in the Manual Job Manager, missing spot color channels (that cannot be found in any of the spot color sets) are listed in the info pane on the bottom of the dialog box. You can then manually assign a spot color from a spot color set to a channel or enter a CMYK value.

However, it is possible to use a multicolor ICC profile as a proof profile for color managing spot color channels instead of using the spot color sets. If a multicolor ICC profile is loaded as a proof profile, the channels defined in the ICC profile will be matched to the image channel names. Found matches will show up in the Color column on the Channels tabbed page. Channels are matched by the ink set name in the profile.

Spot colors from spot color sets can still be assigned (automatically from the spot color set or manually in the Channels page) to channels that are not defined in the multicolor ICC profile. It is also possible to overwrite an existing channel definition by using a spot color set. (This is not possible if Conversion CT/LW is used.)

Multicolor ICC processing.

When creating a job with a multicolor image and loading a Custom multicolor ICC proof profile, GMG ColorProof automatically matches all existing channels in the image (6 c in this example) to existing channels in the multicolor ICC profile with an identical channel (ink) name (1). If a channel is missing in the profile, a spot color from a spot color set can be assigned manually (2) or you can directly define a CMYK value. If a job is generated by a workflow, the program automatically searches for a matching color in the spot color sets assigned to the workflow.

How to apply a multicolor ICC color management

1. Create a new job or set up a new workflow (or edit the Properties of an existing job or workflow).
2. Click the Color Management button on the navigation panel on the left of the Manual Job Manager / Workflow Properties dialog box.
3. Click the Proof Output tab.
4. Select either a Proof Standard with multicolor ICC characterization profile or select Custom from the Proof Standard list.
5. Select Use the following profile, click the browse button and load the desired multicolor ICC profile.
   (This is the input profile, describing the image color space. The output profile (Printer ICC Profile) is defined in the Calibration Set.)
6. Select the Rendering Intent.
7. Click the Channels tab.
8. Check that all input channels could be matched with a profile channel. Reassign channels if necessary by choosing the appropriate color from the Color drop-down list.

Channel Mismatch options

If channels are missing in the ICC profile for processing a selected CMYK+spot color file, the file cannot be processed (job in error status).

On the Channels tabbed page in the Manual Job Manager, you can manually correct the channel assignment. It is possible to reassign any input channels to channels in the ICC file. It is also possible to assign the same ICC channel to multiple input channels.

If a channelexists in the image, but not in the profile, you can do one of the following:

a) Assign a channel existing in the profile. Duplicate channels are possible. Color values of duplicate channels will be multiplied.
b) Assign a spot color definition from a spot color set.
c) Manually enter a CMYK or Lab value (free spot color).
If a channel exists in the profile, but not in the image, you can do one of the following:

a) Assign a channel existing in the profile to any channel in the image, thus overwriting the current color definition of this channel.
b) (Do nothing.) Additional (not used) channels in the profile are ignored.

Label Information

Label information needs CMYK channels for printing. If CMYK channels are not available in the printed image (either because no CMYK channels were present as input channels in the first place, or because they were reassigned to spot color channels), the top color channel in the Channels list is used for printing the label.

Control Strips

The channels present in an image control strip must also be available in the printed image. If not, the control strip cannot be printed together with the image. For spot colors, you can print the GMG Spot Color Control Strip, or load custom spot color control strips into the database (Database view > Control Strips).