Choosing colour profiles for PDF files

[Hedley Finger]

I am trying to understand the use of ICC colour profiles in colour 
management.

My understanding is that any device that can record (camera) or present 
(monitor, inkjet printer, offset printer) has a colour profile 
describing its gamut under specified conditions.

If you are doing colour work on a computer (including graphics in 
publications, retouching or correcting graphics, etc.) then you need to 
associate each input device (camera, scanner) and output device 
(monitor, inkjet printer) with its manufacturer supplied profile or, in 
fanatical cases, a profile specially calibrated for the device using 
suitable input and output targets, colorimeters, etc.  Colour when 
stored in files by a camera, scanner or software program is actually in 
a hue-invariant model such as L*a*b*, and are transformed into a 
particular device colour space when moved to/recorded by/presented by 
that device from another. So far, so good.

But what I do not understand is when programs such as Photoshop, 
Scribus, or InDesign allow you to choose particular profiles to use.  Is 
this simply to provide a preview of how colours will look on a 
particular output device (offset, inkjet), to detect out-of-gamut 
colours, or are colours actually modified in some way when they are 
saved to disk by the program?

If the latter and colours are actually translated within the program 
(Photoshop, etc.), won't they be distorted on the output device when its 
colour profile is applied again by the colour management system (CMS) to 
colours that have already been translated?  A sort of colour 
double-counting if you will?

If you are producing a PDF for a particular combination of printing 
process, CMYK inks, and paper, does, say, a printing profile such as 
SWOP applied to the PDF mean that the PDF file is merely a surrogate for 
the printing press and that no further profile is applied when the 
plates are burned?

Any advice from those more knowledgeable than me is greatly appreciated.

Regards,
Hedley

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Hedley Finger

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