[Numpy-discussion] Help with bit arrays

Henrique Almeida hdante.lnls at gmail.com
Fri Apr 29 12:47:07 EDT 2016


 I think in any case, the result is unexpected, PIL is loading garbage
from memory when loading black and white images because it sends the
wrong buffer size, and matplotlib correctly loads the black and white
image, but stores it in a 3D array.

2016-04-29 13:43 GMT-03:00 Henrique Almeida <hdante.lnls at gmail.com>:
>  For 1 bit images, the resulting array has shape (256, 256, 4). For
> grayscale images, the shape is (256, 256). So the image seems to have
> been loaded as a color image.
>
> 2016-04-29 13:38 GMT-03:00 Benjamin Root <ben.v.root at gmail.com>:
>> What kind of array is "img"? What is its dtype and shape?
>>
>> plt.imshow() will use the default colormap for matplotlib if the given array
>> is just 2D. But if it is 3D (a 2D array of RGB[A] channels), then it will
>> forego the colormap and utilize that for the colors. It knows nothing of the
>> colormap contained in the TIFF.
>>
>> Ben Root
>>
>>
>> On Fri, Apr 29, 2016 at 12:31 PM, Henrique Almeida <hdante.lnls at gmail.com>
>> wrote:
>>>
>>>  Paul, yes, imread() worked for reading the black and white TIFF. The
>>> situation improved, but now, there seems to be some problem with the
>>> color map. Example code:
>>>
>>> #!/usr/bin/env python3
>>> import numpy
>>> from matplotlib import pyplot, cm
>>>
>>> img = pyplot.imread('oi-00.tiff')
>>> pyplot.imshow(img)
>>> pyplot.colorbar()
>>> pyplot.show()
>>>
>>>  The code can open both 1-bit and 8-bit images, but only with 8 bits
>>> the image is shown with the colormap colors. The 1 bit image is shown
>>> as black and white.
>>>
>>>  The questions:
>>>  1) Should Image.open() behave like pyplot.imread() ? Is this a bug in PIL
>>> ?
>>>  2) Why isn't the colormap working with black and white images ?
>>>
>>> 2016-04-29 13:06 GMT-03:00 Paul Hobson <pmhobson at gmail.com>:
>>> > Does using pyplot.imgread work?
>>> >
>>> > On Fri, Apr 29, 2016 at 8:27 AM, Henrique Almeida
>>> > <hdante.lnls at gmail.com>
>>> > wrote:
>>> >>
>>> >>  Any help with this problem ?
>>> >>
>>> >> 2016-04-27 11:35 GMT-03:00 Henrique Almeida <hdante.lnls at gmail.com>:
>>> >> >  Hello, what's the current status on numpy for loading bit-arrays ?
>>> >> >
>>> >> > I'm currently unable to correctly load black and white (1-bit) TIFF
>>> >> > images. Code example follows:
>>> >> >
>>> >> > from PIL import Image
>>> >> > import numpy
>>> >> > from matplotlib import pyplot
>>> >> >
>>> >> > img = Image.open('oi-00.tiff')
>>> >> > a = numpy.array(img)
>>> >> >
>>> >> > ^ does not work for 1-bit TIFF images
>>> >> >
>>> >> > PIL source shows that it incorrectly uses typestr == '|b1'. I tried
>>> >> > to
>>> >> > change this to '|t1', but I get :
>>> >> >
>>> >> > TypeError: data type "|t1" not understood
>>> >> >
>>> >> > My goal is to make the above code to work for black and white TIFF
>>> >> > images the same way it works for grayscale images. Any help ?
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>>
>>
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