Clear distinction between positive and negative in colorbar

Here I am not able to distinguish between positivie and negative (everything is in green from -1 to +1). Can you please help me giving a different color to some set of values and different colors to another set of values. Screenshot is attached below.

I want all negative values to be bluish and darker.

[David Wilson]

You probably want to use caxis, and some appropriate colour maps. I suggest diverging maps, such as the ones from Cynthia Brewer:

https://au.mathworks.com/matlabcentral/fileexchange/34087-cbrewer-colorbrewer-schemes-for-matlab

Say use rdBu and flipud the color map to get blues on the negative scale.

As an example (using peaks), and cbrewer from the user's group. (I note that this latter function probably needs an update, and there are other equivalent ones around now.)

n = 11; % should be odd 
cmap = flipud(cbrewer('div','RdBu',n)); % blues at bottom 
colormap(cmap); 

M = peaks(20); 
pcolor(M)
caxis((n-1)/2*[-1,1]) % align colour axis properly 

colorbar

gives white at the interface:

[Ahmed]

Hi @David Wilson link is not working. can you share the function cbrewer/RdBu?

[David Wilson]

Could try an alternative, say:

ColorBrewer: Attractive and Distinctive Colormaps - File Exchange - MATLAB Central (mathworks.com)

Answer 1

[Rik]

I would suggest using the top half of viridis and the bottom half of plasma (or the reverse). You can get both of them here.

The benefit is that both colormaps are perceptually uniform, should avoid problems for different types of colorblindness and even allow printing in black&white (or actually grayscale).

Using these two colormaps has the advantage that there is a clear color change in the middle between the two. You could insert a white in the middle, but you shouldn't, since that will cause confusion with the top of the colorbar.

viridis_top = viridis;
viridis_top = viridis_top(1:end/2,:);
plasma_bottom = plasma;
plasma_bottom = plasma_bottom(end/2:end,:);
cmap = [viridis_top;plasma_bottom];

colormap(cmap); 

M = peaks(1000);
h = pcolor(M);h.EdgeColor = 'none';
extreme = max(abs(min(M(:))),max(M(:)));
caxis(extreme*[-1,1]) % align colour axis properly 
colorbar

[Ahmed]

@Rik thanks

[Rik]

@Ahmed you're welcome. Since you didn't ask this question originally you can't mark this answer as accepted answer, but if you feel I've helped you, you can also show your appreciation by giving my answer an upvote.

If you have any other question, feel free to post it and tag me in a comment.

[Ahmed]

@Rik thanks, voted, can you plz help to edit the code by including more colors. For example, I want to add more color options in the plot/map.

[Rik]

What exactly do you mean with 'more color options'? And what did you try? You can see in my code how to define a custom colormap and how to set the caxis. What other parts are unclear to you?