[Image-SIG] going between numpy array and PIL.Image not behaving as expected -- how to report a bug ?

[Jim Vickroy]

Ned Batchelder wrote:
> Yes, it definitely looks like a bug in fromarray.  typestr is '<i4' in 
> my environment, and the check against typestr[1:] seems to recognize 
> this.  The line
>
>     typestr = typestr[:2]
>
> should change, perhaps to:
>
>     typestr = typestr[-2:]
>
> --Ned.
> http://nedbatchelder.com
OK, I have been wandering around http://www.pythonware.com/ for a while 
and have somehow missed the URL for bug reporting.  Could someone point 
me in the right direction?  Sorry if I have missed something obvious.

P.S. (Ned)
Thanks for coverage.py; I was a little slow to make the association!
>
> Jim Vickroy wrote:
>> Ned Batchelder wrote:
>>> I'm not sure exactly what you are trying to do here, but the issue 
>>> has to do with the mapping of numpy array elements into pixels.  
>> Thanks for your clear and detailed reply and sorry for the vagueness 
>> of my posting; you did correctly read my mind!
>>> Your code uses 32-bit ints, and fromarray defaults to "L" mode, 
>>> which is 8-bit grayscale pixels.  fromarray uses the shape of the 
>>> array to create the shape of the image, but then just reads bytes 
>>> until the image has all the data it needs.  In your case, it only 
>>> needs to read 3 32-bit ints to get enough bytes to fill the 3x4 "L" 
>>> mode image.  In the first three ints, the min byte is zero and the 
>>> max byte is 2, which your image extrema verifies.
>>>
>>> If you change your code to use this:
>>>
>>>     source  = numpy.arange(0,12,dtype=numpy.int8)
>>>
>>> then everything will match up: your array has byte elements, and 
>>> your image will have byte pixels.
>> Thanks, this does indeed work and your explanation made me wonder why 
>> specifying dtype=int (as in my posted script) did not work. 
>>
>> Here is the signature of PIL.Image.fromarray in my installation (v 
>> 1.1.6):
>>
>>     * fromarray(obj, mode=None)
>>
>> so when mode is not specified, the procedure determines it from the 
>> attributes of "obj" as follows:
>>     if mode is None:
>>         typestr = arr['typestr']
>>         if not (typestr[0] == '|' or typestr[0] == _ENDIAN or
>>                 typestr[1:] not in ['u1', 'b1', 'i4', 'f4']):
>>             raise TypeError("cannot handle data-type")
>>         typestr = typestr[:2] ##### why isn't this: typestr = 
>> typestr[1:] or typestr = typestr[1:3] ? ##################
>>         if typestr == 'i4':
>>             mode = 'I'
>>         elif typestr == 'f4':
>>             mode = 'F'
>>         elif typestr == 'b1':
>>             mode = '1'
>>         elif ndim == 2:
>>             mode = 'L'
>>         elif ndim == 3:
>>             mode = 'RGB'
>>         elif ndim == 4:
>>             mode = 'RGBA'
>>         else:
>>             raise TypeError("Do not understand data.")
>>
>> I  am  relatively inexperienced with both PIL and numpy, but the  
>> statement:
>>
>>     * typestr = typestr[:2]
>>
>> seems to be incorrect; after it is executed, I do not see how typestr 
>> can ever be any of ('i4' , 'f4', 'b1').
>>
>> If I make the indicated change to
>>
>>     * typestr = typestr[1:]
>>
>> then "mode" is correctly inferred from "obj" and I do not have to 
>> explicitly specify it when applying the fromarray() procedure.
>>
>> Is this a logic error in fromarray()?
>>>
>>
>>>
>>> --Ned.
>>
>>>
>>> Jim Vickroy wrote:
>>>> Hello all,
>>>>
>>>> I am having no success getting numpy and PIL to behave as expected 
>>>> when starting with a numpy array (see the attached script).
>>>>
>>>> Here is the output on my computer:
>>>>
>>>> <output>
>>>> Python version: 2.5.2 (r252:60911, Feb 21 2008, 13:11:45) [MSC 
>>>> v.1310 32 bit (Intel)]
>>>> numpy version:  1.2.1
>>>> PIL version:    1.1.6
>>>> numpy source array:
>>>> [[ 0  1  2  3]
>>>> [ 4  5  6  7]
>>>> [ 8  9 10 11]]
>>>> numpy source array shape: (3, 4)
>>>> PIL image size: (4, 3)
>>>> Traceback (most recent call last):
>>>>  File "C:\Documents and Settings\jim.vickroy\My 
>>>> Documents\Projects\GOES\SXI\__trials__\numpy-PIL.py", line 30, in 
>>>> <module>
>>>>    ''' % (extrema, image.getextrema())
>>>> AssertionError:
>>>>   numpy image extrema (minimum,maximum): (0, 11)
>>>>   PIL   image extrema (minimum,maximum): (0, 2)
>>>> </output>
>>>>
>>>>
>>>> I would appreciate pointers on what I'm doing incorrectly.
>>>>
>>>> Thanks,
>>>> -- jv
>>>> ------------------------------------------------------------------------
>>>>
>>>> _______________________________________________
>>>> Image-SIG maillist  -  Image-SIG at python.org
>>>> http://mail.python.org/mailman/listinfo/image-sig
>>>>   
>>>
>>> -- 
>>> Ned Batchelder, http://nedbatchelder.com
>>>   
>>
>
> -- 
> Ned Batchelder, http://nedbatchelder.com
>   

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/image-sig/attachments/20081121/145acfd2/attachment-0001.htm>