Dear John,
>>>>> John Fox <j...@mcmaster.ca>
>>>>> on Thu, 30 May 2013 08:13:19 -0400 writes:
> Dear r-helpers,
> I'm interested in locating the named colour that's "closest" to an
arbitrary RGB colour.
Hmm, maybe I was not really marketing well enough
what I had added for R 3.0.0 :
------------------------------------------------------------------------
r61127 | maechler | 2012-11-17 20:00:58 +0100 (Sat, 17 Nov 2012) | 1 line
new option colors(distinct=TRUE); new demo(colors) & demo(hclColors)
------------------------------------------------------------------------
demo(colors) contains a few niceties, some originating from
------------ Marius Hofert,
notably for you the function nearRcolor()
which has the nice extra that you can specify the color *space*
in which to measure nearness.
##' Find close R colors() to a given color {original by Marius Hofert)
##' using Euclidean norm in (HSV / RGB / ...) color space
nearRcolor <- function(rgb, cSpace = c("hsv", "rgb255", "Luv", "Lab"),
dist = switch(cSpace, "hsv" = 0.10, "rgb255" = 30,
"Luv" = 15, "Lab" = 12))
{
if(is.character(rgb)) rgb <- col2rgb(rgb)
stopifnot(length(rgb <- as.vector(rgb)) == 3)
Rcol <- col2rgb(.cc <- colors())
uniqC <- !duplicated(t(Rcol)) # gray9 == grey9 (etc)
Rcol <- Rcol[, uniqC] ; .cc <- .cc[uniqC]
cSpace <- match.arg(cSpace)
convRGB2 <- function(Rgb, to)
t(convertColor(t(Rgb), from="sRGB", to=to, scale.in=255))
## the transformation, rgb{0..255} --> cSpace :
TransF <- switch(cSpace,
"rgb255" = identity,
"hsv" = rgb2hsv,
"Luv" = function(RGB) convRGB2(RGB, "Luv"),
"Lab" = function(RGB) convRGB2(RGB, "Lab"))
d <- sqrt(colSums((TransF(Rcol) - as.vector(TransF(rgb)))^2))
iS <- sort.list(d[near <- d <= dist])# sorted: closest first
setNames(.cc[near][iS], format(d[near][iS], digits=3))
}
You should use the full
demo(colors)
or browse
https://svn.r-project.org/R/trunk/src/library/grDevices/demo/colors.R
to also get a few nice examples..
Martin
> 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.
>
> Examples:
>
> > rgb2col(c("AA0000", "002200", "000099", "333300", "BB00BB", "#005555"))
> [1] "darkred" "darkgreen" "blue4" "darkgreen" "magenta3" "darkgreen"
> > rgb2col(c("AAAA00", "#00AAAA"))
> [1] "darkgoldenrod" "cyan4"
>
> Some of these colour matches, e.g., "#005555" -> "darkgreen" seem poor to me.
> Even if the approach is sound, I'd like to be able to detect that there is no
> sufficiently close match in the vector of named colours. That is, can I
> establish a maximum acceptable distance in the HSV (or some other) colour
> space?
>
> I vaguely recall a paper or discussion concerning colour representation in R
> but can't locate it.
>
> 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/
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