[R] question in value-based color in image()

Jim Lemon jim at bitwrit.com.au
Wed Sep 17 11:29:07 CEST 2008

M. wrote:
> Hello,
> I have a matrix A with value varying from -1 to 1.  I hope to use scaled
> color based on its value to produce an image of this matrix.
> Suppose I hope to label those data in [-1,-0.5] with blue, label those
> [-0.5,0.8] with light blue (tone is proportional to its value, e.g.
> rgb(1-tone, 1-tone, 1) where tone=abs(A)/0.5), and label those [0.8,1] with
> white.
> How can I use image() and rgb() to achieve this?  It would be great if I can
> have a color scale legend, too.
Hi Chris,
Have a look at color2D.matplot in the plotrix package (particularly the 
last example for more than one color range). I think you will have to 
precalculate your colors and pass that as the "cellcolors" argument.


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