Color map from green to red

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Idan Hamawi
Idan Hamawi on 17 Oct 2020
Edited: DGM on 19 Apr 2022
Hi all,
I have a map with values and i would like to display the values with colors - from green to red.
The value closest to 0 will be green and the farthest will be red.
Example:
1, 5, 11, 33, 56, 100
1 - Green.
100 - Red.
Can be also:
-5, -23, -43, -55, -80.
-5 - Green.
-80 - Red.
The rest values will be in the order and color bar.

Accepted Answer

Akira Agata
Akira Agata on 17 Oct 2020
You can create your original colormap (green to red) and apply to the data.
The following is an example:
% Create green-to-red colormap
cMap = interp1([0;1],[0 1 0; 1 0 0],linspace(0,1,256));
% Apply to the plot
surf(peaks)
colormap(cMap)
colorbar
  4 Comments
Harpreet Singh
Harpreet Singh on 19 Apr 2022
But that is a one way gradient. Didn't Akira want a two way gradient? with gren being in the middle and red going outwards?
DGM
DGM on 19 Apr 2022
Edited: DGM on 19 Apr 2022
I don't really think OP was after an RGB sweep, but more of an HSV hue sweep. Still, if Akira's solution was enough, then it could be made symmetric.
% Create red-green-red colormap
cMap = interp1(0:2,[1 0 0; 0 1 0; 1 0 0],linspace(0,2,256));
% Apply to the plot
surf(peaks)
colormap(cMap)
colorbar
FWIW, for simple RGB primary/secondary sweeps like this, you can improve the linearity to get rid of the dark bands:
% Create red-green-red colormap
cMap = interp1(0:1,[0 1 0; 1 0 0],linspace(0,1,256));
cMap = cMap.^(1/2.4); % linearize
% Apply to the plot
surf(peaks)
colormap(cMap)
colorbar
This gamma adjustment of colormaps can also be done using the misleadingly-named brighten() function, though the parameter behavior is (in my opinion) confusing in the degree to which it obfuscates the otherwise extremely simple math.
Gimme a minute and I'll whip up a colormap that replicates the exact map that OP posted.

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More Answers (1)

DGM
DGM on 19 Apr 2022
Edited: DGM on 19 Apr 2022
This is how one might go about getting the exact colormap shown in the image and make a symmetric version of it.
A = imread('gyrcb.png');
imshow(A)
% get base color table from image
basect = im2double(permute(A(40,24:517,:),[2 3 1]));
N = 256;
nb = size(basect,1);
% interpolate to get a specified-length version
CT1 = interp1(1:nb,basect,linspace(1,nb,N));
% also make a symmetric version of the same length
CT2 = interp1(1:2*nb,[flipud(basect); basect],linspace(1,2*nb,N));
% Apply the new CT
surf(peaks)
colormap(CT1)
colorbar
% Apply the symmetric CT
figure
surf(peaks)
colormap(CT2)
colorbar
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