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

[Bryan Hanson]

Works perfectly!  Thanks Barry.  I had actually seen some suggestions on
using a distance, but by then I was thinking about hcl spaces and distance
isn't so as simple there.  I'm too tired I think.

Anyway, you've got me running again!  Thanks, Bryan


On 10/13/09 5:12 PM, "Barry Rowlingson" <b.rowlingson at lancaster.ac.uk>
wrote:

> 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