Hello Thibaut,
In PDF, ICC-profiles can be attached to individual objects (images, graphics, text) see page 174-175 in the book.
ICC profiles in individual objects cause in most cases an an color transformatin of this objects during the RIP process, which may differs from the transformation when the PDF files is displayed at the monitor or when it will be send to an proof.

One big insolved issue e.g. for colormanagement inside PDF is e.g. the usage of blackpoint compensation, which is not specified in any PDF standard yet, but heavily used in Adobe CS applications.

So most people do not want ICC-profiles in individual PDF objects for a production ready PDF. They prefer a PDF where all objects are defined in CMYK ready for the final printing process. But printing for e.g. offset printing ob coated paper or newspaper needs different kind of CMYK-data.

So PDF allows the usage of an ICC-profile as "output intent" (see page 177 of the book). The output describes the colorspace which the creator intended to be as output. An PDF/X file (X is for Exchange in printing) an output intent must be included in the PDF file. They act only as a description and don´t cause trouble in the RIP.


In Adobe CS 2 and later, the output intent used in the PDF/X presets is taken from the CMYK settings of the application. If you e.g. specify ISOcoated_v2_eci.icc as CMYK-profile in Illustrator, this will be your output intent in every Illustrator PDF/X preset.

Illustrator (different to InDesign) forces the user to create document where all objects of the PDF have the same colorspace.
If you want to be shure, that placed CMYK content will not be color transformed during import into Illustrator, you should use the CMYK color policy CMYK: Preserve numbers (ignore Linked Profiles) see page 176 of the book.

If you want to create PDF/X files with transparencies, you need PDF/X-4 as basic standard. Please note that that is possible to create CMYK only PDF/X-4 with transparencies, but it is also possible to create PDF/X-4 with different colorspaces and ICC profiles in differnt objects. So far as I know, this more important for InDesign than for Illustrator.

But to be shure, it makes a lot of sense to make preflight of the PDF/X-4 file to be CMYK only. The only organisation I know, which have guidelines to create CMYK PDF/X-4 data including preflight is PDF/X-ready with the PDF/X-Ready V2 spec, But currently these specs and guidelines are only available in german. http://www.pdfx-ready.ch/index.php?show=531 (it may will be translated to french in a later step....)

The most important organisation for specs and guidelines based on PDF/X http://www.gwg.org don´t delivers guidelines to create and preflight CMYK PDF/X-4 (But they are working on it since some years...)

For further steps, I would recommend an inhouse training for colormanagement, PDF-creation and PDF preflight, because there is currently no How To guide in french or english available for the things you are doing in daily practice.

Regards
Jan-Peter

PS: More infos about my english book at http://www.colormanagement.de/book-digital-color-management/


Am 09.12.11 09:15, schrieb Thibaut Simonart:
Dear all,
 
I work for a small packaging company whose activity consist of printing (offset), cutting and folding cardboard. Since not long, we have decided to handle PDF files from the client and produce the offset plates ourselves because we had too many problems with external providers. The change has been pretty quick and now that everything is +/- OK, we would like to improve greatly and manage color correctly.
 
I have read many website as well as the “Digital Color Management” book from Jan-Peter Homann, but there are still a few things that remain unclear. It seems obvious that there are a few key elements that I haven’t understood and it will be of great help if you could shed some light on these matters.
 
I have read everywhere that the PDF files sent by the clients should be CMYK that contain no ICC-profile. It still doesn’t make sense for me at the moment. I know I am wrong, but I don’t understand why.
 
1) When you set up a PDF document (eg. in Illustrator or CS Suite), you need to set up you working space. Mine for CMYK documents is defined on “ISO Coated v2 ECI”. What does it do actually ? Does it apply an ICC profile ? Does it transform colors ? I really don’t understand the mechanism ...
 
2) When you export your PDF (I know I should use PDF/X but I do need to keep transparency and separate layers), in the “Output” section.
--> I need to choose “Convert to Destination (Preserve numbers)”
--> Destination should be the same as working space (thus ISO coated v2 ECI) for correct color management
--> ICC profile should not be included
--> Output intent should be defined
 
Is that right ? If it is, here is what I don’t get :
- What is the difference between “Convert to Destination (Preserve numbers)” and “Convert to Destination”. In other words, what does the “Preserve numbers” option actually does ?
- What would change if the ICC profile was included ? How will it inpede color management at the next steps ? I thought a document or image should always have an ICC profile associated so that software knew how to treat it ...
- Does the output intent actually as an impact when opening the files in an application or is it just text information for the viewer that says how it should be printed ?
- Do RGB images previously converted in Photoshop (let’s say for Iso coated) and then inserted in the PDF still contain ICC profile when the PDF is exported ?
 
I am sure you have now realised that I still have not correctly understood color managmeent. This is why I am sending you this mail. Usually I would never do that, but I can’t find the answer anywhere else and I think it’s important to understand these concepts correctly.
I hope some of you can help me Sourire
 
Kind regards,
 
Thibaut SIMONART
 


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