[R] col2rgb() function

[Duncan Murdoch]

On 23/07/2023 2:15 p.m., Nick Wray wrote:
> Hello  I have a palette vector of colour blind colours (in hexadecimal)
> which I’m using for plots, but they are not see-through, and as I wanted to
> overlay some histograms I wanted to convert these colours to rgb, when you
> can set the opacity.
> 
> I have found the function col2rgb(), which works in the sense that it gives
> a vector of numbers but these don’t work directly in rgb because they are
> too big.  If I divide through to make them all less than 1 I don’t get the
> corresponding colour-blind hue, but something somewhat off.
> 
> Here is the colour-blind palette in a plot:
> 
> 
> *cb8<- c("#000000", "#E69F00", "#56B4E9", "#009E73","#F0E442", "#0072B2",
> "#D55E00", "#CC79A7")*
> 
> *plot(0,0,xlim=c(1,8),ylim=c(0,1))*
> 
> *points(1:8,rep(0.5,8),col=cb8,pch=19,cex=2)*
> 
> 
> 
> so if I try to convert the red dot ("#D55E00") (number 7) I get
> 
> *col2rgb("#D55E00"*
> 
>    [,1]
> 
> red    213
> 
> green   94
> 
> blue     0
> 
> *points(7,0.25,col=rgb(rgb(213,94,0)),pch=19,cex=2)*
> 
> gives me an error message and although if  I divide through
> 
> *points(7,0.25,col=rgb(213/307,94/307,0),pch=19,cex=2)*
> 
> gives me a reddish dot, but not the same as in the colour-blind palette

Why are you dividing by 307?  You should divide by 255.

Duncan Murdoch