Put to white the plot space outside a geometric shape

Dear all

I am using the attached colorbar to generate some plots, which looks like this:

As you can see, because the colorbar seems to not assign a plain white color to zeros, the background color outside the geometric shape has some residual color. How could I avoid this problem efficiently?

Answer 1

[Mathieu NOE]

hello

have you checked that the colorbar is symetric around zero (to have white color correspind to zero exactly ? )

this requires to use caxis as in example below (the seond plot is "whiter" than the first one).

RdBu250cbrewer = readmatrix('RdBu_250_cbrewer2.txt');

Z = peaks(100) + 1 ;

% without caxis
figure(1),
imagesc(Z)
colormap(RdBu250cbrewer);
colorbar('vert')

% with caxis
figure(2),
zm = max(abs(Z),[],'all');
imagesc(Z)
colormap(RdBu250cbrewer);
caxis([-zm zm])  % force colors to be used symmetricaly so white correspond to zero 
colorbar('vert')

[Mathieu NOE]

also plain white is rgb = [ 1 1 1] , which does not appear in your color map, as the closest values are like

0.966924490903 0.968909725660 0.970034318301

so it's a bit grey (very very slightly)

[Mathieu NOE]

there are lot's a colormap generators on Fex, for my fun I used this one :

Red White Blue Colormap - File Exchange - MATLAB Central (mathworks.com)

her's the result obtained (code below)

% with redwhiteblue 
% (Fex : https://fr.mathworks.com/matlabcentral/fileexchange/86932-red-white-blue-colormap)
figure(3)
imagesc(Z)
zmin = min(Z,[],'all');
zmax = max(Z,[],'all');
colormap(redwhiteblue(zmin, zmax));
colorbar;

[DGM]

I'll add that the RdBu map never reaches white in the center. It maxes out at [0.9686 0.9686 0.9686]. Since the given map is even length, it never actually includes this neutral color.