How to create a custom dynamic colormap?

Hi,

I have been wondering about how to create a custom colormap, with a dynamic range similar to the default colormaps in MATLAB. The call to the colorbar will be something like,

 customColormap = getCustomColormap(nColors);

It is possible that there is no clear solution to this problems, but it would be great if anyone have an idea to how to proceed.

Best Regards Patrik

Answer 1

[Simon]

Hi!

You can use the command "colormap" to create color maps. The built-in colormaps can be scaled dynamically, like

colormap(jet(nColors))

You can as well build your own color maps. A color map is a m-by-3 matrix of real numbers between 0.0 and 1.0, specifying RGB values.

[Patrik Ek]

Thank you for the answer, but what I really meant was that I wanted to specify an own colormap that could be scaled dynamically. Eg I want three basic colors black green and red and then want to be able to create an algorithm to scale these to a number of variants depending on the size of the colormap. Is there any basic way to do this or do I need to do this by trial and error?

BR/Patrik

[Simon]

Do you know the interactive colormap editor? With this you can build your own color map.

What you can do is: specify your edge colors of the color map. Then you can use matlab's interpolation routines to calculate a custom colomap. The following example might help you.

% taken from "doc surf"
[X,Y,Z] = peaks(30);
surfc(X,Y,Z)
colormap hsv
axis([-3 3 -3 3 -10 5])

% number of colors
n = 20;

% color map with red and blue on the edges
C = [1 0 0; 0 0 1];
% convert to HSV for interpolation
C_HSV = rgb2hsv(C);
% interpolate hue value
C_HSV_interp = interp1([0 n], C_HSV(:, 1), 1:n);
% compose full HSV colormap
C_HSV = [C_HSV_interp(:), repmat(C_HSV(2:3), n, 1)];
% convert back to RGB
C = hsv2rgb(C_HSV);
% set colormap
colormap(C)
colorbar

[Patrik Ek]

Thank you this colormap editor is amazing. For the automatic rescaling I guess i gets more complicated the more advanced colormap, but thank you for giving me a start.

[Giuseppe]

A small correction:

C_HSV = [C_HSV_interp(:), repmat(C_HSV( 1, 2:3), n, 1)];