Re: [Icc_users] Matrix profile with negative "Red colorant tristimulus"
Re: [Icc_users] Matrix profile with negative "Red colorant tristimulus"
- Subject: Re: [Icc_users] Matrix profile with negative "Red colorant tristimulus"
- From: Mark <email@hidden>
- Date: Wed, 17 Sep 2008 13:44:32 +0200
The problem had nothing to do with negative primary XYZ values at all:
the matrix profile was being tagged as LAB PCS instead of XYZ.
I was so irritated by the negative negative values that I didn't see
that.
Thanks a lot Lars.
Best regards
Mark
On 17.09.2008, at 04:33, Lars Borg wrote:
MacOS X Preview doesn't seem to mind negative values.
You probably have other profiles with negative values already
installed.
So your problem is probably somewhere else.
Did you try Profile First Aid to verify?
Lars
At 3:54 AM +0200 9/17/08, Mark wrote:
Thanks for the explanation Graeme.
What is the best way to get rid of the negative XYZ values so I can
use the profile on CMMs that are more strict?
Mark
On 17.09.2008, at 03:04, Graeme Gill wrote:
Mark wrote:
I opened the profile with ColorSync Utility and see the it has
negative values for the "Red colorant tristimulus" Y (-0,005) and Z
(-0,000).
Hum, this is wrong - right? How can the primaries have negative
values?
A matrix is really a transformation into another 3D coordinate
system,
and it's quite possible for that system to have primaries that are
at imaginary, non-real world coordinates (the XYZ coordinates do
this
themselves). If the RAW RGB values from your camera have been
manipulated
by various processing stages in the camera, it is quite possibly
that
the best fitting matrix is one that has primaries that are non-real,
and even have -ve XYZ values.
Unfortunately the ICC format didn't anticipate this situation,
and while
the XYZ values are encoded as signed values, it forbids XYZ values
being negative and some CMM's may enforce this, making the correct
fitting profile matrix illegal as far as they are concerned. Other
CMM's take a more pragmatic view, and allow -ve XYZ values.
Graeme Gill.
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