On Mon, Jun 25, 2012 at 10:03 AM, julien tayon <jul...@tayon.net> wrote:
> Hello,
>
> I made a crude sonogram https://gist.github.com/2983547 with the note
> names instead of the frequency. But, It really angers me not to be
> able to have a log scale for the frequency.
>
> Does any well known workaround exists?
> Is there an easy way to grosso modo do :
> x = time, y = frequency, z=amplitude of spectre with something like a
> specter of one croche at time = t according to the bpm and make an y
> scale logarithmic, then project the amplitude (z) with a colormap on
> x,y plane according to the amplitude, and and have 3D representation?
>
> Basically, I guess it boils down to know if combining those 2 is
> possible :
> http://matplotlib.sourceforge.net/examples/mplot3d/contourf3d_demo2.html
> + log scale for y. I guess I could improve the result by using
> logscale on Z and colormap
> (
> http://stackoverflow.com/questions/5748076/python-matplotlib-contour-plot-logarithmic-color-scale
> )
>
>
> Since it is only for fun, and I don't want to invest myself too much
> my question is really did I missed something while googling for an
> easy solution and if so, what are the good keywords?
>
> Cheers
> --
> Julien
>
>
Julien,
I am not entirely sure if I understood your question right, but I think I
can answer part of it. With respect to using a log scale for 3d axes, it
*should* work, but unfortunately, I have never been able to get it to work
properly. It is an outstanding bug for mplot3d. The "work-around" is to
do the log transformation yourself for the input x/y/z data.
However, there is no reason why you can't use a LogNorm for your colormap.
Just so you understand, color scales in matplotlib are done in two parts.
We have the "Norm" objects which takes data and produce values between 0
and 1 (and handles bad, over, and under values accordingly). And we have
"colormap" objects that take values from 0 to 1 and produce an RGB(A)
array. By default, most functions in matplotlib will use the min/max of
the input data to automatically create a linear Norm object, and will use
the "prism" colormap. However, you can create a LogNorm object and pass it
in as the 'norm' kwarg in most plotting functions.
I hope this helps!
Ben Root
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