Re: Photoshop 6 Duotone Mode, Working Spaces & Profiles
Re: Photoshop 6 Duotone Mode, Working Spaces & Profiles
- Subject: Re: Photoshop 6 Duotone Mode, Working Spaces & Profiles
- From: "Stephen Marsh" <email@hidden>
- Date: Tue, 19 Mar 2002 04:23:46 +1100
Neil B. posed a very good question - which I thought I knew the answers to,
but I was wrong in part and misleading. This post is to correct my original
post, add further information 'for the record' and to spark further comment.
I think this is an important issue - and I have learned a lot from this
initial test. Thanks for the heads up Neil.
* Workflow #1: Duotone mode Photoshop file (quadtone) converted to RGB for
inkjet output.
Duotone inks specified as as _custom colour picker_ builds for the K, C, Y
and the _default library build_ for PMS 158. The KCY plates are entered as
100% solids of the current CMYK work space (the LAB values fall how they
will based on the WS profile).
Change the CMYK setup while in Duotone mode, and the Duotone image changes.
So I was wrong that the values are locked into the Duotone mode
inkset/transfer curves - since there is both a change on the monitor, and
this change also happens to the data (LAB values change for the image, so it
is not just a display issue).
This means that if you change inkset/dotgain in the custom CMYK settings, or
change CMYK profiles - then the Duotone image is hosed. This was not
expected, but ver4, 5 and 6 all behave this way. The display and conversion
from Duotone mode to RGB/LAB/CMYK should _NOT_ be affected by the CMYK
workspace once the Duotone colour picker has been setup. The Spot Working
Space is also affected by the dot gain entered, so this compounds the
results from the CMYK WS. This spot dot gain is factored into conversions
from Duotone to other modes (as expected).
Where I was correct, was in my statement that using the default built in
library inksets in the Duotone colour selector is safe and locks in the LAB
values of the image. So if the image was defined with KCY plates using
default library build Pantone Coated and not custom colour, then the image
would not change colour and luminosity when the CMYK WS is changed. The file
will be affected by the Spot WS settings though, which is logical.
It will take some testing to see what combo of CMYK WS and Spot WS dot gain
settings create the LAB values that are intended via the ink/transfer curve
choices in the Duotone mode options. By this I mean if you have a solid
value in a plate then you expect this to convert to RGB with the correct LAB
value. If you make the 100% transfer curve 50%, you would expect the LAB
values in the RGB conversion to be 50% of the solid ink LAB reading, since
the solid is now being limited to 50%. Depending on the CMYK and or Spot dot
gain settings, you may or may not get a true 'colorimetrically true' 50%
value on conversion. 62L 62A 62B should be 81L 31A 31B for a 50% transfer
(remember that the L is not linear, near gamma 3).
* Workflow #2: Duotone mode Photoshop file saved as EPS and output as
separations from page layout software.
Define the Duotone inks as default Pantone library builds. These have a LAB
description, but when used in default form the hard wired numbers supplied
from Pantone (pre 2000 colour formula) are built into the file. If the
values defined for the ink in question are 0c 60m 94y 0k for PMS 158 - that
is the value that is imported into layout software (since layout and
illustration apps seem to like CMYK builds - even if the original definition
is LAB based).
Alternatively, the user can hit custom and type the displayed LAB values for
the default library build back in again, to force Photoshop to recalculate
the new CMYK values based off the CMYK WS, instead of the hard wired library
CMYK build defined by Pantone. Now the custom CMYK build will be used by
other software when the Duotone mode EPS is imported. This means that if
other software uses default builds for spot colour - it will have to be
synced with the Photoshop values, otherwise composite prints will vary
between the Photoshop Duotone EPS content and the layout or other content.
Although obvious - this may not be the case for all users.
In this workflow, the CMYK and Spot settings have no impact on the Duotone
mode EPS file that goes to separation in layout software. If the transfer
curve wants the PMS 158 plate shadow at 50% - that is the tone that will be
imaged at the RIP. But as indicated, the build that defines the Duotone inks
may have an impact - if the default library build is not used - for
composite output (say digital proofing).
This means that the colour build used for composite prints may have a
different build if the inkset is defined via custom colour picker settings
and the CMYK or Spot settings change during production or in updating
software etc.
It is impractical to only use the default library builds (many users want
better composite proofs), so the CMYK settings do indeed play a critical
role in the use of Duotone mode in two common workflows - both within and
outside Photoshop.
Since there is no way to tag a ICC profile into a Duotone mode EPS, PDF or
PSD - the user is screwed if they ever change settings or software.
Depending on the file, it's visual display in Photoshop and conversions to
other modes in Photoshop are directly related to one or two work space
options, neither of which can be recorded in the ICC world. The only way to
ensure that future use of the archived Duotone file (which is 1/4 the size
of a multi channel quadtone) - is to use the file info notes to list the
active CMYK and Spot WS settings, with inkset and dotgain being the only
variables necessary for legacy custom CMYK engine profiles (GCR/UCR and
black gen is ignored). If you do not change your WS settings on a regular
basis, then an action can be recorded which will enter the appropriate info
found in Colour Settings for future manual reference and matching.
Multichannel mode is no option - since you loose the Duotone edit features
and Multichannel is also affected by the CMYK or Duotone settings, depending
on the build for the inkset colour.
Duotone mode has always had lots of traps and shocks for users, and even
after 10 years of limited use - I am still learning things about how it
behaves when used in different workflows and settings.
It seems that the ICC and Adobe need to integrate Duotone mode better into
the colour managed workflow. It would also be nice if Adobe spelt out what
is really taking place behind the scenes, so that issues like this do not
occur when a user opened up an old archive after updating to new software in
the interim.
Sincerely,
Stephen Marsh.
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