How do I create a logarithmic scale colormap or colorbar?

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

Answer 1

[MathWorks Support Team]

Please follow the steps below to create a log colobar in 'surf' plot:

% Plot the surface plot

[X, Y] = meshgrid(1:0.5:10,1:20);
Z = sin(X) + cos(Y);
figure;
surf(X, Y, Z)

% Show the colorbar

colorbar

% Set the log colobar

set(gca,'ColorScale','log')

Note: This feature was introduced in MATLAB R2018a.

For more information, refer to the following documentation page, "Axes Properties":

https://www.mathworks.com/help/matlab/ref/matlab.graphics.axis.axes-properties.html#budumk7-ColorScale

Answer 2

[lvn]

set(gca,'ColorScale','log')

https://nl.mathworks.com/help/matlab/ref/matlab.graphics.axis.axes-properties.html#budumk7-ColorScale

[jonas]

I'm pretty sure it was introduced in 2018a

[Walter Roberson]

Another approach for R2018a is:

cb = colorbar();
cb.Ruler.Scale = 'log';
cb.Ruler.MinorTick = 'on';

In theory this should also work in R2017b (and perhaps other releases), but in R2017b you will get an warning message,

 Warning: Error updating ColorBar.
   DataSpace or ColorSpace transform method failed

[Walter Roberson]

You can tell by the wording of the official answer that it was written for an older version of MATLAB.

[Pat]

Hi Kristoffer Walker,

If you still need assistance with this issue, please create a MathWorks Technical Support Case. We would be happy to help you out.

https://www.mathworks.com/support/contact_us.html

Answer 3

[Berthold Reisz]

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)