RE: Decoding ColorSync monitor profiles
RE: Decoding ColorSync monitor profiles
- Subject: RE: Decoding ColorSync monitor profiles
- From: Roger Breton via colorsync-users <email@hidden>
- Date: Fri, 22 Nov 2019 22:00:37 -0500
Oopsie, doopsie! I found the colorant tags (rXYZ, gXYZ and bXYZ) from which
I was able to compute the chromaticities and (some) conversion to CIE Lab.
Things are starting to make sense but I suspect I need to invert the
Chromatic Adaptation Matrix to get to D50 CIE Lab values? Right now, the red
primary rXYZ is showing as
X 0.389 Y 0.219 Z 0.039 which translates to x = 0.6012 and y = 0.3385 (not
the same values as those found in the "Native Display Information" tag,
shown below, which was x = 0.5881 and y = 0.3333). Not that "far", mind you,
which makes me suspect that if I was to invert the chromatic adaptation
matrix, I'd probably be close to 0.5881, 0.3333? Forgive me for playing
"sorcerer apprentice" out loud.
/ Roger Breton
-----Original Message-----
From: colorsync-users
<colorsync-users-bounces+graxx=email@hidden> On Behalf Of
Roger Breton via colorsync-users
Sent: Friday, November 22, 2019 9:33 PM
To: ''colorsync-users?lists.apple.com' List'
<email@hidden>
Subject: Decoding ColorSync monitor profiles
I'm in the ColorSync Utility, on a MacBook Air, looking at the "Phosphor"
tab (French MacOS 10.12.6) of the "Color LCD-77E200AD-B0E6..icc" profile.
I'm intrigued by the displayed Red, Green, Blue and White chromaticities:
x y
------ -------- ---------
Red 0.5881 0.3333
Green 0.3229 0.5495
Blue 0.1542 0.0900
White 0.3127 0.3290
White chromaticities are easy to decode, this is straight Rec 709 HDTV D65.
However, the red, green and blue chromaticities are not straight Rec 709.
As you know, these chromaticities are incomplete without the Y = Luminance
factor.
Is there a way, mathematically, to compute the Y from the x and y?
I'm using Robin Myers's excellent ColorConverter 2.2 to "guestimate" the Y
by typing in the x and y values, and trial-and-error different Y factors,
until I hit the "maximum" a* and b* for that color, to get at a "realistic"
CIE Lab value.
Please forgive my technical ignorance.
For the red primary, I get the "max" a* with a Y = 55 value which gives a
CIE Lab value of 79.04 90.28 54.12. Somehow, this "method" of mine does not
make sense? I get a Chroma of 105 and a Hue angle of 31 degrees.
Any help is appreciated.
/ Roger Breton
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