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

[lvn]

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

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

[Chris F]

I've had success with this in version 2018a, but what about 2016a? I get the error: there is no ColorScale property on the Axes class.

[jonas]

I'm pretty sure it was introduced in 2018a

[Callum Walter]

Can confirm 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

[sam ira]

I get this error also in R2018a ...

[Sanat Kumar Tiwari]

@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]

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

Answer 2

[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)

Answer 3

[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

[Samira Daneshgar]

Hi, I would like to know how can I apply the same thing for the contourf. Thanks,

Answer 4

[Jakob Weis]

Digging this oldie up again: As mentioned by Samira, the logarithmic ColorScale option does not seem to be working for contour and contourf. It looks like it's having trouble getting the color levels correct. Sure, an easy workaround is to plot the log10 and manually change the colorbar ticklabels but that doesn't look particularly nice. It'd be great if this got fixed in a future release.

Here's a MWE visualising the problem:

C = 10.^repmat(linspace(-5,5,1000),[1000,1]);

figure(1);clf
tiledlayout(2,2)
nexttile(1)
contourf(log10(C),50,'LineStyle','none')
title('contourf')
clim([-5 5])
cb1 = colorbar;
cb1.Label.String = 'log10(C)';
set(gca,'XTick',[],'YTick',[])

nexttile(3)
contourf(C,50,'LineStyle','none')
set(gca,'ColorScale','log')
clim([10^-5 10^5])
cb2 = colorbar;
cb2.Label.String = 'C';
set(gca,'XTick',[],'YTick',[])
nexttile(2)
p1 = pcolor(log10(C));
p1.EdgeColor = 'none';
title('pcolor')
clim([-5 5])
cb3 = colorbar;
cb3.Label.String = 'log10(C)';
set(gca,'XTick',[],'YTick',[])
nexttile(4)
p2 = pcolor(C);
set(gca,'ColorScale','log')
p2.EdgeColor = 'none';
clim([10^-5 10^5])
cb4 = colorbar;
cb4.Label.String = 'C';
set(gca,'XTick',[],'YTick',[])