Re: Change PCS of CLUT input profile
Re: Change PCS of CLUT input profile
- Subject: Re: Change PCS of CLUT input profile
- From: Mark <email@hidden>
- Date: Thu, 11 Oct 2007 08:29:55 +0200
Hello Graeme, Steve,
thanks a lot for your explanations - reading your posts showed me I
was clearly misunderstanding some basic workings of ICC.
I was under the impression that all output profiles are always XYZ
PCS (the reason is because every output profile I looked so far was
XZY based: sRGB, AdobeRGB, AppleRGB). I overflew most of the latest
ICC spec and I see that assumption was wrong.
So if I understand you both, I should do is create a device link
profile: a merger of the input profile and the output profile. Can
that be done between profiles that use LAB PCS and XYZ PCS (so my LAB
input profile and lets say a XYZ Rec 709 HDTV profile)? What does a
device link profile look like - will all "processing" be merged into
a single A2B tag? That should be fast and accurate.
On the other hand, I now realize that keeping the data in LAB can be
quite nice for manipulating it - I guess it's the best color space
for many manipulations. So I'm thinking about the following workflow:
input RGB x input profile -> LAB -> manipulations -> still LAB ->
output profile -> final RGB
That looks quite nice, I just have to find out how to create CLUT
based output profiles with LAB PCS for whatever destination color
space I need..... where should I look at? Can Argyllcms create such
profiles?
I'm in agreement with Graeme, you should look at the straight
conversion from your source RGB to the destination RGB space. In
the ICC world that's a device link profile (you can read more in
the ICC spec but you may find better information Googling).
If you calculate a device link then the PCS space is used as a
reference but disappears in the result. Then your job is to take
the role of the CMM and move it into the graphics card. The nice
thing is that the heavy lifting will be taken care of and you'll
really just be writing an very efficient interpolator.
It sounds like a reasonable project. I've heard of CMM-style
calculations being moved to the card before so it seems possible.
Beside being a nice umbrella to writing GPU shaders that's what Core
Image is: a GPU based CMM. It is just too obscure and inflexible for
my needs.
Again thanks for helping me newbie out.
Regards
Mark
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