Re: Step-by-step through a CLUT...
Re: Step-by-step through a CLUT...
- Subject: Re: Step-by-step through a CLUT...
- From: Mark <email@hidden>
- Date: Wed, 17 Oct 2007 17:53:05 +0200
Hello Graeme,
I was probably confused by the LCMS tutorial - I read the sections of
the ICC spec again, and well, that added to the confusion:
Section 10.8 lut16Type describes the 'mft2' tag: I see ColorSync is
perfectly right showing Matrix, In Curves, Table and Out Curves, as
these are exactly the 4 operations allowed in 'mft2' (or it's 8 bit
variant 'mft1'). Graeme, you are right, there is enough information
in there to know how to compute the tables.
Now, I wonder what section 10.10 lutAtoBType (tag 'mAB ') is used
for. I could not find any input or output profile that uses these
tags - does anybody have such a profile?
Clearly the stages outlined in LCMS are the possible processing
steps, for the different LUT types - but no profile will actually
have them all.
Thanks for making me read the spec again...
Mark
On 17.10.2007, at 16:39, Graeme Gill wrote:
Mark wrote:
I would just like to add that I read the LCMS tutorial, there LUT
stages are explained as:
[Mat] -> [L1] -> [Mat3] -> [Ofs3] -> [L3] -> [CLUT] -> [L4] -
> [Mat4] -> [Ofs4] -> [L2]
Mat{n} are matrices of 3x3
Ofs{n} are offsets
CLUT is a multidimensional LUT table
Interestingly when I look at a profile in ColorSync, for an A2Bx
tag it shows only the tabs Matrix, In Curves, Table, Out Curves.
Why won't ColorSync display the additional Matrixes and 1d LUTs?
Perhaps the LCMS tutorial is referring to it's complete internal
path, where it is dealing with PCS conversion (Lab <-> XYZ), and/or
absolute intent conversion, and/or it is showing ICCV4 profiles
support, while colorsync is showing the processing for just a V2 lut16
profile table ?
Graeme Gill.
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