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How do I create a logarithmic scale colormap or colorbar?

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I need to color SURF plots on a log scale and subsequently displace the log-based colorbar.

Accepted Answer

MathWorks Support Team
MathWorks Support Team on 17 May 2018
Edited: MathWorks Support Team on 17 May 2018
This answer was flagged by Scott Smith
The ability to create a logarithmic scale COLORMAP or COLORBAR is not available in MATLAB.
A fellow customer posted the following suggested workaround for this problem on our USENET newsgroup, comp.soft-sys.matlab (CSSM):
% D is your data
% Rescale data 1-64
d = log10(D);
mn = min(d(:));
rng = max(d(:))-mn;
d = 1+63*(d-mn)/rng; % Self scale data
image(d);
hC = colorbar;
L = [0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 20 50 100 200 500 1000 2000 5000];
% Choose appropriate
% or somehow auto generate colorbar labels
l = 1+63*(log10(L)-mn)/rng; % Tick mark positions
set(hC,'Ytick',l,'YTicklabel',L);
Note that this method has not been fully tested by MathWorks. MathWorks does not guarantee or warrant the use or content of these submissions. Any questions, issues, or complaints should be directed to the contributing author.

  1 Comment

Samira Daneshgar
Samira Daneshgar on 12 Jan 2017
Hi, I would like to know how can I apply the same thing for the contourf. Thanks,

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More Answers (2)

lvn
lvn on 4 May 2018
Strange official answer, since it is clearly possible in Matlab:
set(gca,'ColorScale','log')

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Sanat Kumar Tiwari
Sanat Kumar Tiwari on 31 Mar 2020 at 2:19
@Ivn, thanks for pointing out simple solution that is working fine. @Walter, your solution also gives similar results but the colorscales need some adjustment for best colorscheme.
It's surprising that official MATLAB answer is "feature not available" !
Walter Roberson
Walter Roberson on 31 Mar 2020 at 2:38
You can tell by the wording of the official answer that it was written for an older version of MATLAB.

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Berthold Reisz
Berthold Reisz on 15 Mar 2019
Try the following:
% let A be your data
A = 100*rand(100,100);
% plot log10 of A
pcolor(log10(A))
% get the minimum and maximum value of A
c1 = min(min(A));
c2 = max(max(A));
% set limits for the caxis
caxis([log10(c1) log10(c2)]);
% preallocate Ticks and TickLabels
num_of_ticks = 5;
Ticks = zeros(1,num_of_ticks);
TickLabels = zeros(1,num_of_ticks);
% distribute Ticks and TickLabels
for n = 1:1:num_of_ticks
Ticks(n) = log10(round(c2)/num_of_ticks*n);
TickLabels(n) = round(c2)/num_of_ticks*n;
end
% set Ticks and TickLabels
colorbar('Ticks',Ticks,'TickLabels',TickLabels)

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