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Bug 620781 - black point compensation often doesn't work correctly
black point compensation often doesn't work correctly
Status: RESOLVED FIXED
Product: GIMP
Classification: Other
Component: Plugins
2.6.8
Other All
: Normal normal
: 2.10
Assigned To: GIMP Bugs
GIMP Bugs
Depends on:
Blocks:
 
 
Reported: 2010-06-06 22:36 UTC by Elle Stone
Modified: 2012-09-17 19:12 UTC
See Also:
GNOME target: ---
GNOME version: ---


Description Elle Stone 2010-06-06 22:36:48 UTC 
Sometimes Gimp 2.6.8 alters tonality when using relative colorimetric rendering intent with black point compensation. The same conversion without black point compensation is OK. Sometimes when using black point compensation the tonality is altered only a little, sometimes a lot. I've written up a complete description documenting all the steps and providing files to download at: http://www.dustystones.com/2010/photo-essays/bpc-issues/black-point-compensation-issues.html. See section 3. 

If I had to guess, I would say that somehow Gimp has tailored black point compensation to work with sRGB (tonality is wrong if you don't use black point compensation with sRGB), and this tailoring is causing black point compensation to fail when the destination space is not sRGB.
Comment 1 Sven Neumann 2010-06-07 20:50:09 UTC 
That would probably be a bug in littleCMS then. What version are you using ?
Comment 2 Elle Stone 2010-06-08 15:33:40 UTC 
(In reply to comment #1)
> That would probably be a bug in littleCMS then. What version are you using ?

I'm using lcms 1.18 from the Ubuntu Lucid repositories. I did
some further checking. It seems showFoto has the same problem.
Cinepaint 0.25 (PPA) doesn't. Neither does lcms v 1.18 utility tifficc. I
also have  lcms v 2.0 installed locally - tificc from lcms v2 doesn't have this
problem, either.
Comment 3 Elle Stone 2012-09-17 18:08:26 UTC 
Upgrading in Gimp 2.9 to lcms2 did fix the issue.
Comment 4 Michael Natterer 2012-09-17 19:12:14 UTC 
Thanks, let's assume this was a bug in lcms1 and get rid of this bug.