[R] grDevices::convertColor XYZ space is it really xyY?
hanson at depauw.edu
Wed Jun 12 22:20:56 CEST 2013
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*D65/D65 # conversion per brucelindbloom.com
Y <- D65
Z <- D65*D65/D65
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!
On Jun 12, 2013, at 2:57 PM, Ken Knonlauch <ken.knoblauch at 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.
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