[R] Log color scale

[vincent at 7d4.com]

Kartik Pappu a écrit :

> However I need to plot my data in a log transformed color scale.  Is
> this possible?  I will be happy to explain further, but basically I
> need to do this because there are large variations in the max and min
> values of my raw data and I am trying to highlight the differences in
> the values at the lower end of my raw data (while still displaying the
> values at the high end of the spectrum for comparison) so if figured
> the best way to represent this on a (RGB) color scale is to do it with
> a log transform.  I do not want to use too many colors because that
> make the figure too busy.
> Any suggestions on how to achieve this.

Don't use too much time to search a good palette, build it yourself.
build your own color palette, specific to your problem.
It's not very difficult, see ?rgb et al.

a small example (not a log scale) :
palblancbleu  = rgb(15:0, 15:0, 15, max=15);
palrougeblanc = rgb(15, 0:15, 0:15, max=15);
palblanc      = rep(rgb(1,1,1), 8);
palRBB        = c(palrougeblanc, palblanc, palblancbleu);

#palRBB = c(
#"#FF0000","#FF1111","#FF2222","#FF3333","#FF4444","#FF5555","#FF6666","#FF7777"
#,"#FF8888","#FF9999","#FFAAAA","#FFBBBB","#FFCCCC","#FFDDDD","#FFEEEE","#FFFFFF"
#,"#FFFFFF","#FFFFFF","#FFFFFF","#FFFFFF","#FFFFFF","#FFFFFF","#FFFFFF","#FFFFFF"
#,"#FFFFFF","#EEEEFF","#DDDDFF","#CCCCFF","#BBBBFF","#AAAAFF","#9999FF","#8888FF"
#,"#7777FF","#6666FF","#5555FF","#4444FF","#3333FF","#2222FF","#1111FF","#0000FF");

# to visualize it
# to visualize a palette

showpal = function(pal=palRBB)
{
n = 200;
fp = matrix(0,n,1);
for (i in 1:n) fp[i,] = i;

par(mar=c(0,0,0,0), mgp=c(0,0,0), ann=F);
image(fp, col=pal);
}

(images at http://7d4.com/r/pal.php)