If they sum to 1 then they are one and the same. Look at how
chromaticity coordinates are defined in terms of the tristimulus
values.
Quoting Bryan Hanson <han...@depauw.edu>:
Thank you Ken.
90% of my problem was missing the factor of 100. I was just
inputing xyY as a test, I wasn't sure whether the docs were being
clear about nomenclature. Speaking thereof, the D65 values used in
the example: I thought they were chromaticity coordinates, but
apparently they are tristimulus values - is that correct?
Thanks again. This solves several problems in a package I am
developing. Bryan
On Jun 12, 2013, at 4:36 PM, Ken Knoblauch <ken.knobla...@inserm.fr> wrote:
You seem to treating the input values as xyY when they should be XYZ
(case matters).
So, I would do something like this
D65 <- c(0.3127, 0.329, 0.3583)
X <- 100 * D65[1]
Y <- 100 * D65[2]
Z <- 100 * D65[3]
XYZ <- data.frame(X = X, Y = Y, Z = Z)
convertColor(XYZ, from = "XYZ", to = "sRGB")
[,1] [,2] [,3]
[1,] 1 1 1
Quoting Bryan Hanson <han...@depauw.edu>:
Ken, I followed your suggestion and perhaps I don't understand
what to expect from convertColor or maybe I'm not using it
correctly. Consider the following tests:
D65 <- c(0.3127, 0.329, 0.3583) # D65 chromaticity coordinates
X <- D65[1]*D65[3]/D65[2] # conversion per brucelindbloom.com
Y <- D65[3]
Z <- D65[3]*D65[3]/D65[2]
XYZ <- data.frame(X = X, Y = Y, Z = Z) # D65 in tristimulus values (?)
colnames(XYZ) <- c("X", "Y", "Z")
tst1 <- convertColor(XYZ, from = "XYZ", to = "sRGB")
tst2 <- convertColor(D65, from = "XYZ", to = "sRGB")
# none of these are 1,1,1, namely white (they are ~ 0.6, 0.6, 0.6)
So it looks like D65, a white standard, does not come back to
something near white in the sRGB space. What am I doing wrong
here, or what do I misunderstand? Please don't say everything!
Thanks, Bryan
On Jun 12, 2013, at 2:57 PM, Ken Knonlauch <ken.knobla...@inserm.fr> wrote:
Bryan Hanson <hanson <at> depauw.edu> writes:
grDevices::convertColor has arguments 'from' and 'to' which can
take on value 'XYZ'. Can
someone confirm
that 'XYZ' is the same as the CIE chromaticity coordinates
are also sometimes refered to
as 'xyY' in
the literature? Or are these the CIE tristimulus values?
It looks to me like the first case is
true, but I
would appreciate hearing from one of the people in
know. Thanks, Bryan
I.'d look at the code or put in some known data to test it,
but XYZ are tristimulus values and xyY are chromaticity
coordinated and the luminance which is the Y tristimulus
value for the CIE 1931 standard observer.
Ken
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Kenneth Knoblauch
Inserm U846
Stem-cell and Brain Research Institute
Department of Integrative Neurosciences
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69500 Bron
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Kenneth Knoblauch
Inserm U846
Stem-cell and Brain Research Institute
Department of Integrative Neurosciences
18 avenue du Doyen Lépine
69500 Bron
France
tel: +33 (0)4 72 91 34 77
fax: +33 (0)4 72 91 34 61
portable: +33 (0)6 84 10 64 10
http://www.sbri.fr/members/kenneth-knoblauch.html
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
