CMYK to Lab bug plug uncorked_2
CMYK to Lab bug plug uncorked_2
- Subject: CMYK to Lab bug plug uncorked_2
- From: Henrik Holmegaard <email@hidden>
- Date: Sun, 8 Apr 2001 18:52:03 +0200
(Begin part 2)
Because the Adobe PDF libraries don't support calCMYK, and because
the Adobe application implementations write calCMYK, it follows that
Adobe applications create Lab when users want device colors. The easy
way out of this would be to have Distiller leave the CMYK object
alone and convert the format of the color space definition that
object references, hence convert CIEBasedDEFG to an ICC type <prtr>
profile.
As we have discussed before here on the List, the ICC specification
allows a vendor to populate a type <prtr> profile with the same LUT
multiplied up to eight times over. That's why Pshop 5X creates barely
legal ICC printer profiles.
The PDF 1.3 specification only says the embedded ICC printer profile
must have an AtoB direction, it doesn't specify the behaviour of the
LUTs in the AtoB direction.
Distiller 5 beta creates an ICC printer profile from a CIEBasedDEFG
CSA, says InProduction v1.0. Meaning that it populates the profile
with one LUT referenced by all eight intents (the profile is very
small, hence the conclusion).
a. If the CIEBasedDEFG in Pshop 5.0, 5.0.2, 5.5 and 6.0 represents
the intent set in CMYK Setup / Color Settings, then Distiller 5
creates a printer profile that is only Perceptual or only Relative
Colorimetric (AtoB0 or AtoB1).
b. If the CIEBasedDEFG in Pshop 5.0, 5.0.2, 5.5 and 6.0 is always
Relative Colorimetric, overriding the user's choice, then Distiller 5
creates a printer profile that is only Relative Colorimetric (AtoB1)
c. The same uncertainty applies to how Photoshop 5.0, 5.0.2, 5.5,
6,0, Illustrator 8.0 and 9.0 and InDesign 1.0 and 1.5 behave wrt the
PostScript Color Management option in the application's own window in
the printer driver.
If the behaviour is Relative Colorimetric, then it is possible to
take CMYK objects and reinstate the lost total ink coverage and black
generation. If it is perceptual then gamut mapping is applied, and
this is not a good idea under the circumstances.
It is also an open question whether the original white point tag is
supported, and therefore whether the printer profile created by
Distiller 5 will behave correctly in a proofing situation.
So Chris, would you please post the behaviour matrix? I'd like to
finish the ABC color cookbook, and I'll promise to include the full
answer -:).
(End part 2)
--
------------------------------------------
Henrik Holmegaard, TechWrite
Stationay +45 3880 0721 - +45 3881 0721
Mobile +45 2178 3959
Toelloesevej 69, 2700 Broenshoej, Denmark
------------------------------------------