Logarithmic axes in imagesc and contour

[Luca Zanotti Fragonara]

Hello, I want to plot the results of a spectrogram in a logarithmic graph (only in x).

Usually I use imagesc to plot the results of my spectrogram function (not the one ot MatLab), because contour is very slow...

In this particular application I would like to plot the results with the x axes in logarithmic scale.

I have used the following code, and it's working:

figure,contour(En,f,S);axis xy
set(gca,'XScale','log')

The same code with imagesc, doesn't work:
figure,imagesc(En,f,S);axis xy
set(gca,'XScale','log')

I don't receive any red error, but just a warning that says "Warning: Negative data ignored"

I think that is a problem with En vector. It is a vector containing the energy in my signal. It is a very little value at the beginning (smaller than 1) and big at the end (bigger than 1).
So, I need logarithm with negative indexes at the beginning: 10^-3 or so on...
Maybe with imagesc I have some trouble in this case? Is there any easy way to awoid this warning?

In fact in the second case I obtain the axes object empty (white), with the xaxis that goes from 10^0 to 10^4, instead than going from 10^-3 to 10^4.

Any suggestions?

Thank you in advance

[Luca Zanotti Fragonara]

"Luca Zanotti Fragonara" <Luca_Z...@libero.it> wrote in message <hu5pva$b22$1...@fred.mathworks.com>...

Is it possible that is due to imagesc need integer values, or something like this?