MATLAB: Use abslolute colormap scale.

colorcolormapheatmapMATLABplot

Hi everyone, I have a quick question. Lets assume that we have a two dimentional matrix and each of its values represents the temperature of that point in a rectangular plate. How can i plot that matrix so as values of 23 and below are plotted with a blue color and values of 47 and up are ploted in red. The inbetween values are plotted using gradiends of those colors just as the normal colormap would?

Best Answer

Hi.

[x,y]=meshgrid(-7:.02:7);
f=x.^2+y.^2;
imshow(f,[23 47])
colormap(jet)

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MATLAB: Saving heatmaps as image

If you are using R2020a, you can use exportgraphics() ans specify the handle of graphic object.

n2E = rand(10); % for example
n2 = rand(10);
% Heatmap1
        subplot(2,1,1)
        heata=heatmap(n2E);
        heata.GridVisible='off';
        colormap(jet)
        heata.ColorbarVisible='off';
        caxis([-0.4440 0.8660 ])
        heata.FontColor='none';
       
%Heatmap2
        subplot(2,1,2)
        
        heatp=heatmap(n2);
        heatp.GridVisible='off';
        colormap(jet)
        heatp.ColorbarVisible='off';
        caxis([0   4095])
        heatp.FontColor='none';
        
%subplot of heatmaps
        ha=get(gcf,'children');
        set(ha(1),'position',[.1 .1 .8 .4])
        set(ha(2),'position',[.1 .5 .8 .5])
        
        exportgraphics(gcf, 'figure.jpg');
        exportgraphics(ha(1), 'subplot1.jpg');
        exportgraphics(ha(2), 'subplot2.jpg');

MATLAB: Personalising contour plot, map colour scheme

Would something like this work for you?:

R = [linspace(0,1,100) ones(1,43) linspace(1,1,100)];
G = [linspace(0,1,100) ones(1,43) linspace(1,0,100)]; 
B = [linspace(1,1,100) ones(1,43) linspace(1,0,100)]; 
cmap = [R(:),G(:),B(:)];  %// create colormap

figure
img = peaks(128);
imagesc(img)
daspect([1 1 1])
colormap(cmap)
caxis([-10 10])
colorbar
% You might also want to look at this:
% colormapeditor

Basically every colormap can be described by a Mx3 matrix, so here I have used linspace to make a colormap that ranges from blue [0 0 1] to white [1 1 1] and then to red [1 0 0]. You can read more about color specification here. You can also see this in action if you run some code like this:

jet(256)

This generates a jet colormap with 256 elements and if you run this in the command window you will see that the output is a 256x3 matrix of color specifications.

You could also check out colormapeditor which lets you edit colormaps as you like:

Hope this helps,

EDIT:

For contour the correct code would be this instead:

R = [linspace(0,1,100) ones(1,43) linspace(1,1,100)];
G = [linspace(0,1,100) ones(1,43) linspace(1,0,100)]; 
B = [linspace(1,1,100) ones(1,43) linspace(1,0,100)]; 
cmap = [R(:),G(:),B(:)];  %// create colormap
figure
img = peaks(128);
contour(img,128)
daspect([1 1 1])
colormap(cmap)
caxis([-10 10])
colorbar

And the result would look like this:

Best Answer

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MATLAB: Saving heatmaps as image

MATLAB: Personalising contour plot, map colour scheme

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