How to get logarithmic colorbar in MATLAB R2012a for 3D surface plot?

I am trying to surface plot using following data with proper colorbar (log scale) but the result dont show color variation. Also, colorbar do not appear in log scale. Please help me out to fix this problem.

n=[2 5 10 15];
I=[1e-4 5e-4 1e-3 5e-3 1e-2 5e-2 1e-1 5e-1 1];
GB_RR=[1.2E26	6E26	2.4E27	6E27	1.2E28	6E28	1.2E29	6E29	2E31; ...
1.4E26	6.5E26	2.62E27	6.3E27	1.3E28	6.7E28	1.5E29	6.5E29	2.5E31; ...
1.53E26	6.72E27	2.84E27	6.9E27	1.5E28	6.9E28	1.9E28	6.64E29	2.7E31; ...
1.73E26	6.85E27	2.96E27	6.9E27	1.65E28	7.1E28	2.2E28	6.84E29	2.92E31];
surf(I,n,(GB_RR))
hold on
n1=[2 5 10 15];
I1=[1e-4 5e-4 1e-3 5e-3 1e-2 5e-2 1e-1 5e-1 1];
GB_RR1=[7.00E+26	8.00E+27	6.00E+28	8.50E+28	9.00E+29	4.00E+30	9.50E+30	7.00E+31	7.00E+32
7.20E+26	8.24E+27	6.30E+28	8.75E+28	9.30E+29	4.50E+30	1.50E+31	7.40E+31	7.40E+32
7.42E+26	8.44E+27	6.50E+28	8.85E+28	9.53E+29	4.85E+30	1.75E+31	7.84E+31	7.94E+32
7.72E+26	8.74E+27	6.80E+28	8.99E+28	9.83E+29	5.00E+30	2.10E+31	7.99E+31	8.30E+32];
surf(I1,n1,(GB_RR1))

[Walter Roberson]

It has been a number of years since R2012a.

If I recall correctly:

h = colorbar();   %used to return an axes
set(h, 'YScale', 'log')

No promises. I do not have R2012a installed to test with at present.

[MUZAFFAR IMAM]

Dear Walter Roberson,

Thank You for your reply. Though the colorbar is appearing in log but actual surface plot is not fllowing the colorbar. Only one colour i.e. the lowest color of colorbar is appearing in plot. Please help me to fix it.

Answer 1

[Walter Roberson]

When you use color mapping, color is always assigned by linear interpolation:

crange = caxis();
cmap = colormap();    %colormap that is in effect right now
numcolor = size(cmap,1);
if value < crange(1)
    colorindex = 1;
elseif value > crange(2)
    colorindex = numcolor;
else
    colorindex = floor((value - crange(1)) / (crange(2) - crange(1)) * (numcolor-1)) + 1;
end
color_here = cmap(colorindex,:);

That is, distance away from the lowest value expressed a linear proportion of the distance between the two color endpoints, and map that by the number of colors available to get the color index.

Always

No matter whether you have set the colorbar axes to draw as log or not, the mapping is always done linear.

What should you do to have a log-based color representation?

This: calculate the color or color indices yourself and pass it as the CData to surf. For example,

C = log10(GB_RR) - 25;
surf(I, N, GB_RR, 'CData', C, 'edgecolor', 'none')

[Aurelien Gregor]

So is it possible to get a log-based color representation and a logscale colorbar ?

[Walter Roberson]

You could supply whatever cdata you want and also set the colorbar y scale.

I seem to recall that they added an additional way to change the colorbar scale but I would need to recheck.