Why is DeviceCMYK object getting assigned ICC profile at print time?

On behalf of Adobe's Acrobat Engineering organization:

Simply stated, PostScript printers and especially the implementation of same by various PostScript printer providers do not support ICC color management at all and there especially are problems if you combine any color management with content that has transparency. The PostScript language does not support live transparency.

As such, for printing PDF from Adobe Reader or Acrobat (for a number of releases) has been for the Color Handling setting under Color Management (under Advanced) to be set to Acrobat Color Management as the default. Changing that value to either Same as Source (No Color Management) or No Color Management is strongly not recommended as it may result in severe color distortions and/or transparency flattening artifacts.

The Color Profile under Color Management by default is set to whatever the “working CMYK” ICC color space as determined in your Reader or Acrobat preferences with one exception. For PDF/X files, that color space is set to the color space and uses the ICC color profile specified in the PDF/X file's Output Intent.

All DeviceCMYK colors in the PDF file are passed through to PostScript “as is.”

All DeviceGray color assumed to be in the “working grayscale” ICC color space as determined in your Reader or Acrobat preferences and then treated as color-managed grayscale.

All DeviceRGB colors are assumed to be in the “working RGB” ICC color space as determined in your Reader or Acrobat preferences and then treated as color-managed RGB.

All color managed CMYK, grayscale, RGB, and LAB is converted from its explicit (or assumed) color space to the CMYK color space as described above with an important exception. There are three options that modify the manner in which the color conversion occurs:

Treat grays as K-only grays. With this option, defaulted “on” by default except for PDF/X files:

(1) All conversions from ICC color managed grayscale result in CMYK=(0,0,0,k), i.e. only black colorant, and conversion is such that g=0 yields k=1 and g=1 yields k=0.

(2) All conversions from ICC color managed RGB for which the R, G, and G values are equal (including text and vector objects as well as for all raster images for which r=g=b for every pixel in the raster image), i.e., r=g=b, result in CMYK=(0,0,0,k), i.e. only black colorant, and the conversion is such that r=g=b=0 yields k=1 and r=g=b=1 yields k=0. The avoids unexpected “rich black” colorants (i.e., black printed with combinations of cyan, magenta, yellow, and black process colorants).

Preserve Black. With this option, defaulted “on” by default except for PDF/X files, all conversions of CMYK to C'M'Y'K' in which CMYK=(0,0,0,k) results in C'M'Y'K'=(0,0,0,k'). This preserves black colorant purity and the likely possibility of unexpected rich blacks due to the 4-3-4 transformations that occur in CMYK to C'M'Y'K' ICC color management.

Preserve CMYK Primaries. This option is an extension of the Preserve Black option, defaulted “off” by default, in which for all conversions of CMYK to C'M'Y'K', all pure colorants are maintained. CMYK=(c,0,0,0) results in C'M'Y'K'=(c',0,0,0). CMYK=(0,m,0,0) results in C'M'Y'K'=(0,m',0,0). CMYK=(0,0,y,0) results in C'M'Y'K'=(0,0,y',0). CMYK=(0,0,0,k) results in C'M'Y'K'=(0,0,0,k').

However, there are circumstances where PostScript printer manufacturers provide what we can best describe “secret sauce” color mangement features in the combination of their drivers and RIPs/DFEs to supposedly “improve” the color and second guess what the designer was trying to do. If you are getting unexpected color casts, you should try turning any proprietary driver color settings to off or disabled. Likewise, turn off any attempts of the printer to assume colorant overprinting where it was specified in your original CMYK content. The only printer color settings that may be useful or helpful is if the printer offers to match the assumed color space of your CMYK. For example, if the Color Profile specified per above is set to U.S. Web Coated (SWOP) v2 and your printer has a matching emulation setting, you may achieve better color matching by setting that printer setting (or equivalent in the printer driver setup).

          - Dov

PS:     FWIW, I was personally involved with the Acrobat engineering team, Adobe's PostScript printing group, and some of our major OEM partners including Xerox to specify, design, implement, and test the change to Acrobat Color Management as the default and the three special options described above. The vast majority of “color issues” experienced by Reader/Acrobat users printing to PostScript printers were resolved as a result of these changes / additions.