[SciPy-dev] ndimage problems

Christopher Hanley chanley@stsci....
Tue Jul 3 11:25:55 CDT 2007


Hi,

We have found two problems with ndimage.  I have filed a ticket #455 on 
the scipy trac page.  The first problem can be seen with this example:

 > import numpy as n
 > from scipy import ndimage as nd
 > a = n.ones((10,5),dtype=n.float32) * 12.3
 > x = nd.rotate(a,90.0)
 > x
Out[17]:
array([[ 12.30000019,  12.30000019,  12.30000019,  12.30000019,
        12.30000019,  12.30000019,  12.30000019,  12.30000019,
         0.        ,   0.        ],
      [ 12.30000019,  12.30000019,  12.30000019,  12.30000019,
        12.30000019,  12.30000019,  12.30000019,  12.30000019,
        12.30000019,  12.30000019],
      [ 12.30000019,  12.30000019,  12.30000019,  12.30000019,
        12.30000019,  12.30000019,  12.30000019,  12.30000019,
        12.30000019,  12.30000019],
      [ 12.30000019,  12.30000019,  12.30000019,  12.30000019,
        12.30000019,  12.30000019,  12.30000019,  12.30000019,
        12.30000019,  12.30000019],
      [ 12.30000019,  12.30000019,  12.30000019,  12.30000019,
        12.30000019,  12.30000019,  12.30000019,  12.30000019,
        12.30000019,  12.30000019]], dtype=float32)
}}}

Notice that the last two entries of the first row are now 0.

The second problem has to do with the reversing of byte order if you 
have big-endian data on a little endian machine.  Please see the example 
below:


 >>> a = N.ones ((2,3), dtype=N.float32) * 12.3
 >>> a = a.byteswap()
 >>> a.dtype = a.dtype.newbyteorder (">")
 >>> print a
[[ 12.30000019 12.30000019 12.30000019]
[ 12.30000019 12.30000019 12.30000019]]
 >>> print ndimage.rotate (a, 90.)
[[ 0.00000000e+00 -4.28378144e+08]
[ 0.00000000e+00 -4.28378144e+08]
[ -4.28378144e+08 -4.28378144e+08]]

I have taken a look at the ndimage python code and cannot find any 
explicit calls to byteswap.  I'm guessing something is funny in one of 
the c-api calls.  I haven't been able to track it down yet.

Chris





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