Re: Display Tweaking
Re: Display Tweaking
- Subject: Re: Display Tweaking
- From: Chris Heinz <email@hidden>
- Date: Mon, 5 Feb 2001 13:28:07 -0500
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As a rule if you want to edit something then only edit the forward
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Lab to device CMYK perceptual gamut mapping in the CMYK production
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profile, never the colorimetric back transform from device CMYK via
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CIELab to monitor device RGB and proofer device CMYK.
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Henrik Holmegaard
I respectfully disagree. There is sometimes good reason to edit the
CMYK-LAB transform of an output profile. In Kodak user doc, we refer to
this as the input transform of the output profile. The reason: this is the
transform used to interpret a CMYK image, to bring it into PCS, so that the
image can be displayed or re-targeted to another printing system (as you
say, 'via CIELab to monitor device RGB and proofer device CMYK').
If the LAB-CMYK transform is edited (the output transform), then separation
results through the profile are modified, and the return display of CMYK to
the monitor corresponds to the change in the separations data. This is the
more common edit, as users attempt to tune the input to output match, or
impart a shop-preferred subjective "look" to their output reproductions.
Conversely, the CMYK-LAB edit support is appropriate if the print is
optimized but the monitor display of the CMYK device image data (and/or the
re-targeted print) is not an optimized match. This edit mode does NOT
affect the way images print through the output profile, but does affect the
display or re-targeted print. [Note: for display, Photoshop 6 uses the
Colorimetric rendering intent, so that is the selection to make when tuning
the soft proof.]
The same principle holds for RGB output devices.
One of the big challenges (and opportunities) for shops with multiple
devices trying to achieve a consistent look is to apply edits judiciously
so the the overall system remains in balance. As an example, let's say you
are trying to proof an Approval CMYK data set on an inkjet printer, and the
match isn't acceptable. In this case, you can tune either the Approval
CMYK-LAB or the Inkjet LAB-CMYK to improve the match. However, if you
tune the Approval CMYK-LAB, when the Inkjet profile is the true issue, then
the soft proof display of Approval CMYK images will inadvertantly suffer
(assuming the user cares about optimized soft proofing).
To realize the goal of device-independent color management, it is important
to keep a 1:1 relationship between the profile and the device...rather than
addressing the deficiencies of one device by editing another device's
profile. In my personal opinion, making the right judgement call is still
far too subjective. At the moment, here is a lot of powerful
functionality/knobs out there that can be mis-used due to a lack of parity
in the feedback mechanisms. Using an auto analogy, there are plenty of:
engines (CMMs)
chassis (ICC-enabled applications)
fuel types (profiles)
and there are not enough context-sensitive 'dashboard displays', smart
diagnositic tools, etc. This latter development category is a reasonable
next step for ICC vendors to consider. There are some positive trends in
this direction (Chromix, ICCtools..) but more is needed - today's statistic
reports should become tomorrow's color advisor...
.........................................................................
Chris Heinz Eastman Kodak Co.
email@hidden Kodak Professional Systems and Solutions
(V)(978) 323-7606 900 Chelmsford St MailCode: MC06352
(F)(978) 323-7680 Lowell, MA 01851 KMX/Knet 276-7606