[R] Opposite color in R

[ken knoblauch]

peter dalgaard <pdalgd <at> gmail.com> writes:

> 
> 
> > On 25 Jul 2015, at 21:49 , Atte Tenkanen 
<attenka <at> utu.fi> wrote:
> > 
> > Hi,
> > 
> > I have tried to find a way to find opposite 
or complementary colors in R.
> > 
> > I would like to form a color circle with R 
like this one: http://nobetty.net/dandls/
colorwheel/complementary_colors.jpg
> > 
> > If you just make a basic color wheel in R, 
the colors do not form complementary color circle:
> > 
> > palette(rainbow(24))
> > Colors=palette()
> > pie(rep(1, 24), col = Colors)
> > 
> > There is a package ”colortools” where 
you can find function opposite(), but it doesn’t work as is
> said. I tried
> > 
> > library(colortools)
> > opposite("violet") and got green instead of yellow and
> > 
> > opposite("blue") and got yellow instead of orange.
> > 
> > Do you know any solutions?
> 
> Not directly, but a few hints: 
> 
> First read up on "complementary colors" in
 Wikipedia. In particular, note that the traditional color
> circle does not satisfy the modern definition 
of opposite-ness. E.g. red paint mixed with green paint is
> brown, not black or grey.
> 
> The construction of the color circle is simple
 in principle: red, blue, yellow go at 0, 120, 240 degrees, the
> other colors on the circle are formed by mixing
 two primaries in varying proportions: green (at 180 deg) is
> an equal mixture of blue and yellow, violet 
(at 60 deg) of blue and red, orange (at 300 deg) 
of red and yellow.
> Blue-green (at 150 deg) would be half blue, 
half green, alias three quarter blue, one quarter
 yellow. Etc.
> 
> The tricky bit is that the above mixtures are 
subtractive mixtures (mixing paint rather than light beams)
> and I don't know how to make a subtractive 
color mixture in the additive RGB space 
that we usually work in.
> Maybe there are tools in the colortools package?
> 
> -pd
> 
> > 
> > Atte Tenkanen

To start with, you should be specifying your "colors"
or lights actually in an additive color space like
CIE 1931 xy,
https://en.wikipedia.org/wiki/CIE_1931_color_space
which you can do in the colorspace package.
But this is based on an average observer and
the results are unlikely to match a given 
individual's vision.  On top of that, decisions made
when this norm was specified are such that it
deviates from human vision for short wavelengths
so that you would be better off using a corrected
version like that proposed by Judd in the 1950's
or for the most recent suggestion see
ww.cvrl.org
under 
New CIE XYZ functions transformed 
from the CIE (2006) LMS functions

best, 

Ken

-- 
Kenneth Knoblauch
Inserm U846
Stem-cell and Brain Research Institute
Department of Integrative Neurosciences
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France
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