R devel - Sep 2008 - question in value-based color in image()

Hello,

I have a matrix 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) 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.

TIA,
Chris

	[[alternative HTML version deleted]]

Please do use R-help, (not R-devel)
for such questions.
>>>>> "M" == M  <glycob at gmail.com>
>>>>>     on Mon, 15 Sep 2008 22:42:22 -0400 writes:
    M> Hello, I have a matrix with value varying from -1 to 1.
    M> I hope to use scaled color based on its value to produce
    M> an image of this matrix.

    M> Suppose I hope to label those data in [-1,-0.5] with
    M> blue, label those [-0.5,0.8] with light blue (tone is
    M> proportional to its value) and label those [0.8,1] with
    M> white.

    M> How can I use image() and rgb() to achieve this?  It
    M> would be great if I can have a color scale legend, too.

    M> TIA, Chris

    M> 	[[alternative HTML version deleted]]

M. wrote:
> Hello,
> 
> I have a matrix 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) 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.

1. This is a message for R-help (if at all), definitely not for R-devel!
2. Have you read ?image ?

Anyway, example:

image(matrix(c(-1, -0.6, -0.4, 1), ncol = 2),
       breaks = c(-1, -0.5, 0.8, 1),
       col = c("blue", "lightblue", "white"))

Uwe Ligges



> TIA,
> Chris
> 
> 	[[alternative HTML version deleted]]
> 
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