Re: Change PCS of CLUT input profile
Re: Change PCS of CLUT input profile
- Subject: Re: Change PCS of CLUT input profile
- From: Steve Upton <email@hidden>
- Date: Thu, 11 Oct 2007 01:32:39 -0700
At 8:29 AM +0200 10/11/07, Mark wrote:
>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,
Ah, I see. Yes most display (and virtual display/working space) profiles tend to use XYZ and the PCS units. Most print profiles (what most of us on this list tend to think of as output profiles - more perspective than correctness) tend to use Lab.
>I should do is create a device link profile: a merger of the input profile and the output profile.
right
> 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)?
yes. The CMM typically worries about stitching them together so you don't need to worry about differing units.
>What does a device link profile look like - will all "processing" be merged into a single A2B tag?
exactly
>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
yes but be careful with Lab. It's a reasonable exchange space but manipulations in it can expose its flaws. De-saturating blue, for instance will turn them purple if you simply move in polar coordinates.
>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?
Yes, Argyll or LittleCMS can do it as well as a number of commercial apps.
Feel free to contact me off-line / off-list if you like.
regards,
Steve
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