Re: [R] col2rgb() function

[Ben Bolker]

  You could also adjustcolor for this approach (levels of red, green, 
blue, alpha can all be adjusted proportionally)

On 2023-07-23 5:35 p.m., David Stevens via R-help wrote:
Nick,
I've also made colors transparent by pasting the hex equivalent of, say,
0.3*256 = 76.9 to the hex color code. e.q. for black it might be
"#0000004d" and the 4d is 77 in hex. That way you don't need to convert
back and forth so much. If col is "#000000" the transparent version is

tcol <- paste0(col,"4d")

This would work in one step on a whole palette.

David

David K Stevens, PhD, PE, Professor
Civil and Environmental Engineering
Utah Water Research Laboratory
Utah State University
8200 Old Main Hill
Logan, UT 84322-8200
david.stev...@usu.edu
(435) 797-3229 (office)

On 7/23/2023 1:00 PM, Nick Wray wrote:
Thanks That works nicely  Nick

On Sun, 23 Jul 2023 at 19:26, Ben Bolker <bbol...@gmail.com> wrote:

     Does adjustcolor() help?

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)
points(1:8,rep(0.75,8),col=adjustcolor(cb8, alpha.f = 0.3), pch=19,cex=2)

On 2023-07-23 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



Somewhat mystified.  Can anyone help?? Thanks Nick Wray

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