Hi,
I have a question about using Bruce Lindbloom's UP Lab color space with lcms. I would like to convert images with embedded profiles into this space, do some manipulations, and then back again to write the output files.
Have taken a look on Bruce Linbloom site... found this paragraph: "The A2B0 tag of the profile converts from CIE Lab to UP Lab. The B2A0 tag performs the inverse transformation."
Unfortunately this is the reverse way to do things, and thus the profile is unuseable. Not only on lcms, but on any CMM. Problem is, used in this way UPLab would be understood as the PCS by the CMM, and ICC only supports XYZ and CIELab as PCS.
But if what you want is a perceptually uniform space to do image processing, I strongly suggest to use CIECAM02 instead. There is an implementation of CAM02 in lcms, you could also build a ColorSpace profile in few steps if you need faster performance.
Regards, -- Marti Maria The littlecms project. www.littlecms.com
----- Original Message ----- From: "Andrew C Mihal" <[EMAIL PROTECTED]>
To: <lcms-user@lists.sourceforge.net>
Sent: Monday, April 25, 2005 3:09 AM
Subject: [Lcms-user] Using Lindbloom's UP Lab color space
Hi, I have a question about using Bruce Lindbloom's UP Lab color space with lcms. I would like to convert images with embedded profiles into this space, do some manipulations, and then back again to write the output files.
The profile for UP Lab has device class "ColorSpace". The A2B0 tag has the CIELab to UPLab transform, and the B2A0 tag goes from UPLab to CIELab. Stop me if I'm going astray... I've been poking in the source code for cmsCreateProofingTransform and cmsCreateMultiprofileTransform to see if they will give me a transform from the input color space to Lab and then to UPLab, but it seems they won't.
Say for example the input space is sRGB. If I make a transform with the input profile=sRGB and the output profile=UPLab, I'm guessing it is going to go from sRGB -> PCS and then it's going to want to use the B2A0 tag in the UP Lab profile to go from the PCS to the output space. Which is backwards. I think I need a "transform-and-a-half", that is to say sRGB->Lab and then Lab to the PCS of the UPLab profile.
I expect there is a good reason why Lindbloom's profile has UP Lab where the PCS usually goes and regular Lab where the output usually goes. But I don't understand what it is. Can someone tell me the right way to do this?
Thanks, Andrew
--------------------------------- Andrew Mihal www-cad.eecs.berkeley.edu/~mihal [EMAIL PROTECTED]
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