The problem is, lcms cannot guess which direction to use.
Let's imagine you have a input profile from RGB to Lab,
and then you connect the colorspace profile after that, finally
you have an output profile implementing Lab ->RGB
Which direction to use?
Well, lcms line of reasoning is something like:
"Ok, here I have a Lab space and then I have to connect it
to da profile... let's try the input direction, oh, great, it matches
the Lab space, ok, let's verify what happens to the output ..
wow, also matches the Lab requirement of output, excellent!"
And then fails miserably to detect the correct direction.
Is for that reason Lab->Lab profiles are usually marked as
abstract profiles. Those have only one direction. Just to
prevent such kind of things.
Also, If I recall correctly, Lindbloom's profile deals with
a tweaked Lab, so I wonder if the profile should be tagged
as using Lab at all. That's not the Lab space all we are used.
Regards
Marti.
----- Original Message -----
From: "Kai-Uwe Behrmann" <[EMAIL PROTECTED]>
To: "Lcms Liste" <[email protected]>
Sent: Wednesday, May 25, 2005 9:25 AM
Subject: [Lcms-user] Lab->Lab spac conversion?
Hi,
I looked at the spec and it says nothing about the above conversion in a
colour space profile. Is Lab not valid as source colour space?
Lcms seems to use the A2B0/B2A0 table pair only in one direction,
ignoring in the other. The result is string hue casts while the gray axis
remains stable.
Anyway with renaming the colour space from Lab to RGB the profile works.
It is about Lindbloom's Uniform Perceptual Lab profile.
regards
Kai-Uwe Behrmann
+ development for color management
+ imaging / panoramas
+ email: [EMAIL PROTECTED]
+ http://www.behrmann.name
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