[R] General means of matching a color specification to an official R color name

[Barry Rowlingson]

On Tue, Oct 13, 2009 at 9:43 PM, Bryan Hanson <hanson at depauw.edu> wrote:
> Hello List Dwellers:
>
> I¹ve looked around quite a bit, but don¹t quite see an answer that I
> understand.
>
> I¹m looking for a way to take any kind of color specification (rgb, hsv,
> hcl, hex) and match it to the n-nearest R official color names.  Clearly it
> is easy to interconvert different specification schemes and color spaces,
> but matching to the name seems a bit trickier.  Seems like if one has a
> specification, it could be fuzzy-matched to the list of official R colors
> expressed in the same specification.  Unfortunately, I don¹t know much about
> fuzzy matching.
>
> For example, following some examples I found in the archives and the wiki, I
> wrote this little function to create a table of official R colors and sort
> it if desired:
>
> colorSpecTable <- function(col = colors(), sort = NULL){
>    require(gplots)
>    rgbcodes <- t(col2rgb(col))
>    names <- col
>    hex <- col2hex(col)
>    df <- data.frame(name = names, hex.code = hex, rgbcodes)
>   # additional elements for other color spaces could be added
>    if (!identical(sort, NULL)) df <- sort.data.frame(df, by = sort)
>    }
>
> Note that sort.data.frame is from the R-wiki and is appended below.  Is
> there a clever way to search a table created by this function, and identify
> the n-closest colors based upon some reasonable criteria?  What I hope for
> is something like this:
>
> colorMatch <- function(hex = NULL, n, plot = HOPEFULLY) {
>    df.rgb <- colorSpecTable(sort = ~red+green+blue) # master table
>    # now search for the n closest matches of hex in df.rgb$hex.code
>    # perhaps hex should be converted into a different color space 1st
>    # eventually would like to display matches side by side w/hex
>    }

 You just need to define your distance in colour space. Simplest might
be a euclidean distance in three-dimensional r,g,b coordinates,
something like:

nearColour <- function(r,g,b){
  ctable = col2rgb(colors())
  cdiff = ctable - c(r,g,b)
  cdist = cdiff[1,]*cdiff[1,]+cdiff[2,]*cdiff[2,]+cdiff[3,]*cdiff[3,]
  return(colors()[cdist == min(cdist)])
  }

 This gives colour names nearest to r,g,b triples, with possible
multiple results:

 > nearColour(0,0,0)
 [1] "black" "gray0" "grey0"
 > nearColour(1,1,1)
 [1] "black" "gray0" "grey0"
 > nearColour(255,255,255)
 [1] "white"   "gray100" "grey100"
 > nearColour(128,0,0)
 [1] "darkred" "red4"

Any good? You could also do it in hsv space, but there's probably
enough colours in the colors() vector that it wouldn't make much
difference...

Barry