www/ IccGreyObjects

Better handling of grey objects in ICC workflows for the graphic arts

Which realworld usecases are adressed

Problems concerning grey objcts in ICC workflows are especially connected with colormanagement of images or complete documents targeting CMYK printing processes. In most cases grey objects are either ignored in the colormanagement workflow or they are converted through the PCS to CMYK. In the very most cases, users are expecting grey objects to be converted to the black channel only of the CMYK printing process.

which kind of applications are targeted

  • layout applications
  • vectorgraphic applications
  • imaging applications
  • pdf workflow applications
  • digital asset management
  • content management systems with output for printing

how should it be implemented technically

If data from different sources is converted trough the source-profile to the PCS (mostly CIE L*a*b*), the CMM doesn´t know if the source colorspace was e.g. RGB, CMYK or Grey. Firstly, we need a mechanism, which tells the CMM, that the actual data converted to the PCS was original a Grey file. Second, we need a mechanism, that the CMM is able to calculate temporarly a greyscale-profile from the blackplate of the destination CMYK-profile. If the data in the PCS colorspace is tagged as Grey, the conversion to the destination-colorspace should be done with the temporarly calculated greyscale-profile instead of the CMYK-destination profile.

how should it be implemented in the user interface

In most cases, such options could be implemented in the menue specifying the destination colorspace for a colortransformation. Good naming would be:

  • convert grey objects only to the black channel In many cases, grey objects have no embbeded profiles. If such objects are placed in a CMYK-document, the user expects grey objects to handled like the black channel of the CMYK document-space. In this case it would be helpful, if the colorsettings for the document have a menue with two options concerning grey objects:

  • preserve embedded greyscale profiles

  • keep grey objects without embedded profiles like the black channel of the CMYK documentspace. If greyscale objects without embedded profiles are converted to the destinationspace, following things should happen: - a greyscale profile is temporarly calculated from the document CMYK-colorspace - The greyscale object is tagged with the temporarly grey document colorspace - After been transformed to the PCS the object has an tag to be original a greyscale object - Being transformed to the destination colorspace, the temporarly calculated destination-greyscale profile is used.

comments from ICC members

The statement that in most cases users are expecting grey objects to be converted to the black channel of the CMYK printing process is certainly correct. The method proposed is one possible approach. Enhancements to this basic method can be considered for certain types of grey objects. For example, the tonescale contrast of greyscale raster images may need to perform differently than the black channel of a particular CMYK profile. Ann ?McCarthy, ICC Workflow WG Chair [note that these comments do not represent a statement of the ICC]

implementations in Open Source solutions

not yet available

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