Customize a colormap

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  1. Hello,I would like to customize a colormap to be able to have four regions. Example, for x>1 (red); for 0.1<x<1 (orange); for 0.01<x<0.1 (yellow); for x<0.01 (green).It can be linear interpolated between the intervals or just plain simple.Any help is appreciated.Thanks,Hugo Policarpo

Accepted Answer

Paulo Silva
Paulo Silva on 26 Aug 2011
maybe this
c=zeros(64,3);
c(1:16,1)=1; %red
c(17:32,1)=1; %orange
c(17:32,2)=0.5; %orange
c(33:49,1)=1; %yellow
c(33:49,2)=1; %yellow
c(50:end,2)=1; %green
load flujet
imagesc(X/max(X(:)))
colormap(c)
  2 Comments
Hugo Policarpo
Hugo Policarpo on 26 Aug 2011
First of all thanks!
the upside-down part is quite straight foward. What I've been battling with is to associate the data intervals with the colors.Just like I stated before,Example, for x>1 (red); for 0.1<x<1 (orange); for 0.01<x<0.1 (yellow); for x<0.01 (green).

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More Answers (2)

Walter Roberson
Walter Roberson on 26 Aug 2011
colormaps cannot be used like that, not unless you are able to define a strict lower and upper bound on x. pseudocolor works by mapping the lowest data value to the lowest color, and the highest data value to the highest color, with everything in-between linearly interpolated according to (x-min(x)) .* (number_of_map_entries ./(max(x)-min(x)))
If you want particular fixed data values to map to particular colors, then you will need to either use RGB instead of pseudocolor (choosing the RGB color yourself), or else you will need to create a color map that has as many entries as different states you want and then map your data to the state number before submitting it to be plotted.
  2 Comments
Hugo Policarpo
Hugo Policarpo on 26 Aug 2011
I'll try your sugguestion Walter.
Thanks

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Daniel Shub
Daniel Shub on 26 Aug 2011
mesh(peaks)
colorbar
set(gca, 'CLim', [0, 1.01])
set(gcf, 'ColorMap', [0, 1, 0; repmat([1, 1, 0], 9, 1); repmat([1, 0.5, 0], 90, 1); [1, 0, 0]])
  2 Comments
Daniel Shub
Daniel Shub on 26 Aug 2011
See my edit. It now gives the correct answer without any "rounding" issues.

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