Things about color management that are not clear - ECI-EN

9 Dec 2011

      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 

Kind regards,

Thibaut SIMONART