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
------------------------------------------------------------------------
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--
Ned Batchelder, http://nedbatchelder.com
_______________________________________________
Image-SIG maillist - Image-SIG@python.org
http://mail.python.org/mailman/listinfo/image-sig
