[Numpy-discussion] array is not writable

[Skipper Seabold]

On Wed, Aug 26, 2009 at 11:49 PM, Mark Wendell<mark.wendell at gmail.com> wrote:
> Figured this much out: if I do an np.copy of the original array to a
> new array, then I can edit individual 'color' values with impunity. So
> I guess the original array from the pil object still shares memory
> with that image object somehow, making it unwritable?
>
> thanks
> Mark
>
> On Wed, Aug 26, 2009 at 7:48 PM, Mark Wendell <mark.wendell at gmail.com> wrote:
>>
>> Hi all - I'm playing with editing image data converted from PIL objects, and running into a situation where numpy tells me that an 'array is not writable'. Not sure I understand what that means, or how to get around it. Here's a sample interactive session:
>>
>> >>> import Image
>> >>> import numpy as np
>> >>> im = Image.open("rgb.0001.jpg")
>> >>> a = np.asarray(im)
>> >>> a.shape
>> (512, 512, 3)
>> >>> a.dtype
>> dtype('uint8')
>> >>> a[0,0,0]
>> 254
>> >>> a[0,0,0] = 10
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in <module>
>> RuntimeError: array is not writeable
>>
>>
>> Any help appreciated. Thanks,
>> Mark
>>
>> PIL 1.1.6
>> numpy 1.2.1
>> Ubuntu 9.04
>>

Hi Mark,

I don't really know the specifics of why your array isn't writeable
(someone will have a better answer and will correct me if I'm wrong),
but you could try to check if it's writeable by doing:

>>> a.flags # or a.flags.writeable

And check the value of writeable.  It might be as simple as setting
a.flags.writeable = True, but then again there might be a good reason
why it's unwriteable.  I don't really know.

Skipper