Re: custom CMYK inks in Photoshop: set relative to D65 ?
Re: custom CMYK inks in Photoshop: set relative to D65 ?
- Subject: Re: custom CMYK inks in Photoshop: set relative to D65 ?
- From: <email@hidden>
- Date: Wed, 14 Dec 2005 21:29:15 -0500
Mike,
Thanks for your pertinent information!
It does indeed seem to jump to the "nearest common"
illuminant when playing with xy values for the White.
Also, if I enter a* = 0 and b* = 0 for the White, I obtain
the coordinates of the nearest illuminant in "xy" mode;
i.e. if xy is near, but not at, D50, fixing a* and b* to
zero changes the xy to the ones of D50; if xy is near, but
not at, D65, fixing a* and b* to zero changes the xy to
the ones of D65.
By default, paper white is near D65, which explains my
observations.
Now my question could be rephrased to: Since SWOP is
defined for D50, why would paper white be near D65?
Because of the expected fluorescence of the paper?
Danny
On Wed, 14 Dec 2005 15:27:34 -0600
email@hidden wrote:
Hi Danny,
Interesting observation! But notice that the Yxy -> Lab
conversions are
dependent on what xy chromaticity is entered for Paper
White (W). If it is
closer to D50 (.345, .358) the conversions are via D50
illuminant. If it
is closer to D65 chromaticity (.313, .329) the
conversions are via D65
illuminant. There is a sudden transition somewhere
about half way in
between.
Another Curious Quirk of Custom CMYK!
Mike Rodriguez
PreMedia Technologies
RR Donnelley
-----Original Message-----
Message: 15
Date: Wed, 14 Dec 2005 14:12:03 -0500
From: <email@hidden>
Subject: custom CMYK inks in Photoshop: set relative to
D65 ?
To: email@hidden
Message-ID: <email@hidden>
Content-Type: text/plain; charset="ISO-8859-1";
format="flowed"
To all,
While making a check, I looked at the ink coordinates
for
SWOP coated in Photoshop. They can be shown in either
xyY
or L*a*b*, which is selected by a small checkbox in the
dialog.
I always assumed that, Photoshop always using the ICC
PCS,
and especially when selecting inks for CMYK profiles,
this
would be defined in D50. However, when converting from
xyY
to L*a*b* and vice-versa, my calculation match Photoshop
only when I used D65, not D50.
Is there a sort of default illuminant PS uses to handle
these values? and which is automatically set set using
my
display profile or something else?
I could not find any doc on this.
Thanks,
Danny Pascale
email@hidden
www.BabelColor.com
Danny Pascale
email@hidden
www.BabelColor.com
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