John Fox <jfox <at> mcmaster.ca> writes:
> I'm interested in locating the named colour that's "closest" to an
arbitrary RGB colour. The best that I've
> been able to come up is the following, which uses
HSV colours for the comparison:
>
> r2c <- function(){
> hexnumerals <- 0:15
> names(hexnumerals) <- c(0:9, LETTERS[1:6])
> hex2decimal <- function(hexnums){
> hexnums <- strsplit(hexnums, "")
> decimals <- matrix(0, 3, length(hexnums))
> decimals[1, ] <- sapply(hexnums, function(x)
> sum(hexnumerals[x[1:2]] * c(16, 1)))
> decimals[2, ] <- sapply(hexnums, function(x)
> sum(hexnumerals[x[3:4]] * c(16, 1)))
> decimals[3, ] <- sapply(hexnums, function(x)
> sum(hexnumerals[x[5:6]] * c(16, 1)))
> decimals
> }
> colors <- colors()
> hsv <- rgb2hsv(col2rgb(colors))
> function(cols){
> cols <- sub("^#", "", toupper(cols))
> dec.cols <- rgb2hsv(hex2decimal(cols))
> colors[apply(dec.cols, 2, function(dec.col)
> which.min(colSums((hsv - dec.col)^2)))]
> }
> }
>
> rgb2col <- r2c()
>
> I've programmed this with a closure so that hsv gets
computed only once.
>
>
> I vaguely recall a paper or discussion concerning colour representation in
R but can't locate it.
>
Dear John,
Are you thinking of
Zeileis A, Hornik K, Murrell P (2009). “Escaping RGBland:
Selecting Colors for Statistical Graphics.” Computational
Statistics & Data Analysis, 53, 3259–3270.
doi:10.1016/j. csda.2008.11.033.
or the vignette from the colorspace package that covers some
of the same territory.
How about if you compute color distances in Lab or Luv spaces?
These so-called uniform color spaces are based on human
discrimination data for small color distances so should be
better at finding the nearest color, I would think. Untried
though. Don't forget that these are based on a standard
color calibration, sRGB, I think in the case of R and your
display may or may not be close to that, so expect some
error from that as well.
best,
Ken
> Any suggestions would be appreciated.
>
> John
>
> ------------------------------------------------
> John Fox
> Sen. William McMaster Prof. of Social Statistics
> Department of Sociology
> McMaster University
> Hamilton, Ontario, Canada
> http://socserv.mcmaster.ca/jfox/
>
>
--
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
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