question in value-based color in image()

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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.
RGB is not the most convenient color space for doing such computations, 
HCL is color model that is quite useful and the package "vcd" provides 
some functions like diverge_hcl() for computing palettes based on HCL 
colors. See
   vignette("hcl-colors", package = "vcd")
   ?diverge_hcl

hth,
Z
TIA,
Chris

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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.

Jim