Re: CMYK to Lab bug (part 1)
Re: CMYK to Lab bug (part 1)
- Subject: Re: CMYK to Lab bug (part 1)
- From: Henrik Holmegaard <email@hidden>
- Date: Sun, 11 Mar 2001 11:44:53 +0100
'It appears that they (: Adobe) added the PostScript Color Management
checkbox in the Save as EPS dialog box in order to dream up some
interest in their technology. When this is turned on, Photoshop
includes an ICC profile in the EPS file. If you've got a PostScript
output device that knows about profiles, it can manage the data
'appropriately'. Otherwise, the printer should ignore it' (Real World
Photoshop 5, page 582).
This is not correct. I first discussed the EPS format with Ron
Gentile in 1997 in order to understand the dual color space
specification support which also bugs PDF.
a. A PostScript RIP does *not* support the ICC color space
specification format. It only supports the device color specification
and CIEBased color space specification.
b. Photoshop embeds a CIEBasedDEFG four channel CSA *as well as* the
whole ICC profile. Simply create a doodle in CMYK mode, save it to
disk as an ASCII EPS, and open it in Word (that's the beauty of ASCII
-:)).
The ICC profile is ignored in the RIP, of course.
The CIEBasedDEFG CSA is applied in the RIP (if the RIP is post 2017).
How the CIEBasedDEFG CSA is applied is defined by the RIP programmer
using what in PostScript is called color rendering procedures. A CSA
is a source color space characterization. When the RIP looks through
the PostScript code and finds a CSA, it grabs that object into CIEXYZ
and the programmed rendering procedure gets applied.
If the RIP is pre 2017, it can't handle a CIEBasedDEFG CSA. A pre
2017 RIP can only handle a three channel CSA.
c. Other applications embed the ICC profile and *not* a CIEBasedDEFG
CSA. Not even Illustrator does that, as I have said a good many times.
The description of printing and the in-RIP color management workflow
in Real World Photoshop 4 is not helpful, either.
I think the problem overall is that there's just too much babying of
Adobe users and ICC color management for that matter. The simple fact
is that Photoshop requires a very very high level of technical
sophistication, or you don't know what you've got. Parts of it are
hopelessly undocumented and the only people who know how it works are
the in-house engineers. That's OK, they should know, of course, but
I'd like to see them tell the rest of us, too.
Either Adobe does a clean sweep and kills the CIEBased color space
specification format in its applications, or we all get a proper
description of what's implemented, where its implemented, and how its
implemented.
--
Henrik Holmegaard
TechWrite, Denmark