col2rgb {grDevices}R Documentation

Color to RGB Conversion


“Any R color” to RGB (red/green/blue) conversion.


col2rgb(col, alpha = FALSE)


col vector of any of the three kind of R colors, i.e., either a color name (an element of colors()), a hexadecimal string of the form "#rrggbb", or an integer i meaning palette()[i].
alpha logical value indicating whether alpha channel values should be returned.


For integer colors, 0 is shorthand for the current par("bg"), and NA means “nothing” which effectively does not draw the corresponding item.

For character colors, "NA" is equivalent to NA above.


an integer matrix with three or four rows and number of columns the length (and names if any) as col.


Martin Maechler

See Also

rgb, colors, palette, etc.


col2rgb(c(blu = "royalblue", reddish = "tomato")) # names kept

col2rgb(1:8)# the ones from the palette() :

col2rgb(paste("gold", 1:4, sep=""))

## all three kind of colors mixed :
col2rgb(c(red="red", palette= 1:3, hex="#abcdef"))

##-- NON-INTRODUCTORY examples --

grC <- col2rgb(paste("gray",0:100,sep=""))
table(print(diff(grC["red",])))# '2' or '3': almost equidistant
## The 'named' grays are in between {"slate gray" is not gray, strictly}
col2rgb(c(g66="gray66", darkg= "dark gray", g67="gray67",
          g74="gray74", gray =      "gray", g75="gray75",
          g82="gray82", light="light gray", g83="gray83"))

crgb <- col2rgb(cc <- colors())
colnames(crgb) <- cc
t(crgb)## The whole table

ccodes <- c(256^(2:0) %*% crgb)## = internal codes
## How many names are 'aliases' of each other:
table(tcc <- table(ccodes))
length(uc <- unique(sort(ccodes))) # 502
## All the multiply named colors:
mult <- uc[tcc >= 2]
cl <- lapply(mult, function(m) cc[ccodes == m])
names(cl) <- apply(col2rgb(sapply(cl, function(x)x[1])),
                   2, function(n)paste(n, collapse=","))
## Not run: 
 if(require(xgobi)) { ## Look at the color cube dynamically :
   tc <- t(crgb[, !duplicated(ccodes)])
   table(is.gray <- tc[,1] == tc[,2] & tc[,2] == tc[,3])# (397, 105)
   xgobi(tc, color = c("gold", "gray")[1 + is.gray])
## End(Not run)

[Package grDevices version 2.5.0 Index]