Getting the primaries of a profile
Getting the primaries of a profile
- Subject: Getting the primaries of a profile
- From: Adriaan van Os <email@hidden>
- Date: Fri, 19 Oct 2018 08:18:37 +0200
I need to get the primaries of an ICC profile. For example, for sRGB the
required values are
Red Green Blue
x 0.64 0.30 0.15
y 0.33 0.60 0.06
I assume that with v1 profiles, these values were given by the 'chrm' tag (see
<https://developer.apple.com/documentation/applicationservices/1560273-0_profiles?language=objc>)
Als this tag seems to be v1 only, for v2 and v4 profiles, I looked at the 'rXYZ', 'gXYZ' and 'bXYZ'
tags instead. However, each ICC document I looked at, gives another definition of these tags, e.g.
for 'rXYZ'
ICC v2, ICC.1 2001-04
"Relative XYZ values of red phosphor or colorant."
ICCv4, ICC1v43_2010-12
"This tag contains the first column in the matrix, which is used in matrix/TRC
transforms."
iccMAX, ICC.2-2018
"The colorEncodingParamsStructure ceptRedPrimaryXYZMbr element represents the nCIEXYZ values of
blue colour space encoding primary encoded using either 2 or 3 numbers. The first value represents
the x chromaticity. The second value represents the y chromaticity. The third value (if present)
represents the z chromaticity. If only two numbers are present the z chromaticity is assumed to be
the value of one minus the sum of the two numbers. If three values are present the sum of the three
values shall be 1.0."
When I look at sRGB IEC61966-2.1 with the ColorSync Utility, I see that the 'rXYZ', 'gXYZ' and
'bXYZ' tags actually represent the values of a Bradford-corrected transformation matrix from sRGB
D65 to XYZ D50.
Can someone please clarify ?
Thanks for the help.
Regards,
Adriaan van Os
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