Color map from green to red

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.

Answer 1

[Akira Agata]

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

[Idan Hamawi]

Thank you! :)

[Brad Atkins]

Thank you

[Harpreet Singh]

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]

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.

Answer 2

[DGM]

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

Similar questions:

colorbar extraction (a discrete colormap)

https://www.mathworks.com/matlabcentral/answers/1591314-how-to-make-colormaps-like-the-attached-colorbar

colorbar extraction (includes notes about dealing with compression artifacts)

https://www.mathworks.com/matlabcentral/answers/1622300-how-to-create-rainbow-colormap-with-violet