[argyllcms] Re: XYZ CLUT profiles
- From: Gerhard Fuernkranz <nospam456@xxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 25 Jan 2010 20:14:03 +0100
Klaus Karcher wrote:
> Hi Graeme,
>
> Did you already notice that Apple's "Profile First Aid" (ColorSync
> Utility) moans about missing tags in Argyll XYZ CLUT profiles?:
>
> Tag 'rXYZ': Required tag is not present.
> Tag 'gXYZ': Required tag is not present.
> Tag 'bXYZ': Required tag is not present.
> Tag 'rTRC': Required tag is not present.
> Tag 'gTRC': Required tag is not present.
> Tag 'bTRC': Required tag is not present.
>
> I'm not exactly well versed in the ICC specs but I think Apple is
> wrong. Also SampleICC's iccProfLibTest tool attests that the profile
> in question is valid.
At least recent versions of the (V4) spec don't require any TRC or
matrix present in "LUT-based display profiles":
"8 Required tags
[...]
8.4 Display profiles
8.4.1 General
This class of profiles represents display devices such as monitors.
The types of profiles available for use as display profiles are
N-component LUT-based, Three-component matrix-based, and Monochrome.
8.4.2 N-Component LUT-based display profiles
In addition to the tags listed in 8.2 an N-component LUT-based input
profile shall contain the following tags:
AToB0Tag (see 9.2.1) and
BToA0Tag (see 9.2.6).
AToB1Tag (see 9.2.2), AToB2Tag (see 9.2.3), BToA1Tag (see 9.2.7),
BToA2Tag (see 9.2.8) may also be included in an N-component
LUT-based display profile. If these are present, their usage shall
be as defined in Table 21 (see 9.1). A gamutTag (see 9.2.18) may be
included. The usage of this tag is identical as in output profiles.
[...]"
But older versions of the spec (for instance "Specification
ICC.1:2001-04" - profile version 2.4.0) seem to require them generally
in "RGB display profiles":
"6.3.2.2 RGB Display Profiles
Table 25 — RGB display profile required tags
Tag Name General Description
profileDescriptionTag Structure containing invariant and localizable
versions of
the profile name for display
redColorantTag Relative XYZ values of red phosphor
greenColorantTag Relative XYZ values of green phosphor
blueColorantTag Relative XYZ values of blue phosphor
redTRCTag Red channel tone reproduction curve
greenTRCTag Green channel tone reproduction curve
blueTRCTag Blue channel tone reproduction curve
mediaWhitePointTag Media XYZ white point
copyrightTag 7-bit ASCII profile copyright information
[...]
*Additional* multidimensional tags (AToB0Tag, AToB1Tag, AToB2Tag,
BToA0Tag, BToA1Tag, BToA2Tag) may also be included. If these are
present, their usage shall be as defined in Table 20.
[...]"
Regards,
Gerhard
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