[Matplotlib-users] imagsc comparison

2009-11-28 Thread Brian Larsen
Hello all, 

several of my colleagues and I are 99% sure we are making the change from IDL 
to python-matplotlib.  I have just one issue that I am trying to work out that 
I need to solve.  We are so far really impressed and looking forward to the 
change.

I have seen discussion on this list about imagesc and imshow but none of them 
have quite answered the questions.  In IDL we spent way too much time writing 
an clone that is still not full featured:
http://people.bu.edu/balarsen/IDLdoc/imagesc.html

I have data of probability distributions which have an X and Y array associated 
with the axes of the 2-d distribution (image).  What I don't see how to do in 
any easy fashion is plot this data in a imshow() manner with the axes correct 
(which are unevenly distributed and need to be plotted on a log axes).  

This can be done with contourf(X,Y,Z) but this has a few issues:
- I dont see how to do a log axes on a contour
- contour is the wrong plot as the inherent smoothing that a contour does is 
highly undesirable.

Using matlab imagesc one can easily make plots similar to:
http://img269.yfrog.com/i/2dprob.png/
Imagine taking the above plot and make the pixels different sizes so that 
each pixel has identical counting statistics.  Now assume that one wanted the 
Y-axis to be plotted in log.

Anyone have any thoughts or toy examples?

Thanks much, 

Brian






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Brian A Larsen
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Boston University
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T: 617-358-4945
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balarsen --at -- bu.edu 




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Re: [Matplotlib-users] imagsc comparison

2009-11-28 Thread Eric Firing
Brian Larsen wrote:
 Hello all, 
 
 several of my colleagues and I are 99% sure we are making the change from IDL 
 to python-matplotlib.  I have just one issue that I am trying to work out 
 that I need to solve.  We are so far really impressed and looking forward to 
 the change.
 
 I have seen discussion on this list about imagesc and imshow but none of them 
 have quite answered the questions.  In IDL we spent way too much time writing 
 an clone that is still not full featured:
 http://people.bu.edu/balarsen/IDLdoc/imagesc.html
 
 I have data of probability distributions which have an X and Y array 
 associated with the axes of the 2-d distribution (image).  What I don't see 
 how to do in any easy fashion is plot this data in a imshow() manner with the 
 axes correct (which are unevenly distributed and need to be plotted on a log 
 axes).  
 
 This can be done with contourf(X,Y,Z) but this has a few issues:
 - I dont see how to do a log axes on a contour
 - contour is the wrong plot as the inherent smoothing that a contour does is 
 highly undesirable.
 
 Using matlab imagesc one can easily make plots similar to:
 http://img269.yfrog.com/i/2dprob.png/
 Imagine taking the above plot and make the pixels different sizes so that 
 each pixel has identical counting statistics.  Now assume that one wanted 
 the Y-axis to be plotted in log.
 
 Anyone have any thoughts or toy examples?

I am not sure I understand exactly what you want to do, but it sounds 
like pcolormesh would do it.  e.g. with ipython -pylab:

ax = gca()
ax.set_yscale('log')
x = np.arange(10)**1.5
y = np.arange(20)**1.8
z = x[1:] * y[1:, np.newaxis]
pcolormesh(x, y, z)
axis('tight')

Note that with x and y, which can be 1-D or 2-D, you are specifying the 
grid boundaries, not the pixel centers.

Eric



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