I sent a PDF of a Pages document for professional printing. The color came out wrong. The printer tells me it is because the document is in RGB format, which I assume is the default for Pages, and must instead be converted into CMYK (process color) for accurate color printing. Anyone know if/how this can be accomplished?
Technically, this is completely incorrect. It is completely incorrect because you will get double CMYK to CMYK conversions which can cause assorted artifacts. Here is the correct workflow:
1. You import into Pages photographs as RGB colour captures from the camera/scanner or colour corrections from the monitor with the ICC device profile for the RGB camera/scanner/monitor state embedded in the RGB images. Therefore, you have specified the input COLOURS your COLOURANTS should form.
If you only place RGB COLOURANTS without embedding the ICC scanner/camera/monitor profile then you have not specified the COLOURS they should form. In this case, ColorSync assigns the Generic CMYK Profile as otherwise you get a dreadful, disastrous RGB to CMYK conversion in PostScript (try RGB to CMYK in QuarkXPress 3 and you will see what I mean).
2. Having placed photographs with RGB colourants and having embedded in each photograph the correct ICC profile for the scanner/camera/monitor, you next embed the ICC profile for the intended printing condition. Adobe applications call this profile the 'CMYK Working Space', ISO calls it the OutputIntent - there are many names but the meaning is precisely the same.
You have now unified the colour management for the printing master. You have set up an input with three channel RGB colourant that is colour managed but not converted, and you have set up the four channel CMYK colourant condition you intend to convert into. Then you leave it at that and had that to the printer as a colour managed printing master.
If you place photographs as CMYK with embedded source ICC profile, and if the ICC profile you set up as OutputIntent is DIFFERENT than any or all of the ICC source profiles, the photographs you preconverted will be converted again into the ICC profile for the outputintent. If you place photographs as CMYK without embedded source ICC profile, you may or may not get a double conversion.
Overall, a professional printer knows what ink limit, graybalance, shadow formation and highlight formation is correct for the printing condition which includes the printing paper. This is why the printer is supposed to publish an ICC profile for the colourants that will form the colours the print shop is selling to customers ('look, we can print these colours and you can proof them up front').
The default format for the pictures inserted in Pages is the format you import them with. Import a CMYK picture and it will stay CMYK.
As they should, but beware of placing preseparated CMYK because the assumption is that preseparated CMYK should be reconverted in order to unify the colourant behaviour for the specific printing condition. If that assumption is lifted, you could place CMYK1 with 200% ink limit, CMYK2 with 250% ink limit, CMYK3 with 300% ink limit and CMYK4 with 400% ink limit and then expect these ink limits to be laid down by the numbers on the press.
'CMYK' is a meaningless abbreviation. The order in which the inks are laid down, the amount of ink in the primary, secondary, terteriary ... combinations, and the colours those pure inks and ink combinations form needs to be specified. If you lay down K black before you lay down Y yellow, which is what is done in some printing conditions, you get a different colour in the secondary combinations of Y and K, for instance. This is not rocket science, it is plain horse sense.
However, it does not convert anything to CMYK. It just makes sure there are embedded colour profiles that can be used by the printer to make proper conversion to CMYK on their side.
The rule is that deviceColor with no source colour specification does not cause a reconversion, but ICCBased with a source colour specification does cause a reconversion.
So the ICC architecture does convert, if the 'CMYK' that is placed in Pages has a source CMYK profile embedded. Whether that is the correct CMYK profile for the colourants, an incorrect profile that was embedded by blindly picking some ICC 'CMYK' profile and sticking it into the colourant file in an image editor, or automatically assigned in the form of the Generic CMYK Profile in some process.
Again, the assumption is that the printer wants to unify the colourant behaviour for the printing condition. This is why 'CMYK' should be converted, if it is not the 'CMYK' for the intended printing condition. Who wants underinking which produces an tiny gamut, or overinking which produces smearing? And who wants grays that are off balance, clogged shadows ... ?
Be aware that the old rule of GIGO (Garbage In/Garbage Out) applies. If your photos are too low a resolution and not color balanced or sharpened they will not print well.
Garbage In/Garbage Out is indeed a problem, which is why we have the ICC architecture in the first place. Always place colour managed CIELab/RGB and convert to the colour managed printing condition to get the correct colourants for the colours offered by the print shop.
Only if you distrust the printer should you preseparate, but if you preseparate to an assumed inking behaviour, you are taking responsibility for the optimisation that the printer is supposed to be selling. How do you know that this is the optimisation for which the printing system is set up for? You don't, so you don't take that responsibility.
I seem to have shopped this little lecture for so many years that I can reel it off in my sleep.
/hh
