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From: Oscar Benjamin <oscar.j.benjamin@gmail.com>
Date: Tue, 12 Mar 2013 14:59:09 +0000
Subject: Re: Reversing bits in a byte
To: Robert Flintham <Robert.Flintham@uhb.nhs.uk>
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On 12 March 2013 13:28, Robert Flintham <Robert.Flintham@uhb.nhs.uk> wrote:
> Sorry, the subject line was for a related question that I decided not to =
ask, I forgot to change it when I changed my email.  I've changed it now!
>
> I'm using Python 3.3 on Windows with the pydicom module (http://code.goog=
le.com/p/pydicom/).  Using pydicom, I've ended up with a "bytes" object of =
length (512*512/8 =3D 32768) containing a 512x512 1-bit bitmap (i.e. each b=
yte represents 8 pixels of either 1 or 0).  When I print this to screen I g=
et:
> 'b\x00\x00\x00.....'
>
> I can unpack this to a tuple of the integer representations of binary dat=
a, but that doesn't really help as presume I need the binary (8 digit) repr=
esentation to be able to translate that into an image.
>
> I wasn't sure which GUI library to use, so haven't specified one.  As it'=
s Python 3, Tkinter is available.  I also have matplotlib and numpy install=
ed, and PIL.
>
> Ideally, I'd like to be able to access the pixel data in the form of a nu=
mpy array so that I can perform image-processing tasks on the data.
>
> So now that I've explained myself slightly more fully, does anyone have a=
ny thoughts on how to do this?

Numpy and matplotlib will do what you want:

import numpy as np
import matplotlib.pyplot as plt

def bits_to_ndarray(bits, shape):
    abytes =3D np.frombuffer(bits, dtype=3Dnp.uint8)
    abits =3D np.zeros(8 * len(abytes), np.uint8)
    for n in range(8):
        abits[n::8] =3D (abytes % (2 ** (n+1))) !=3D 0
    return abits.reshape(shape)

# 8x8 image =3D 64 bits bytes object
bits =3D b'\x00\xff' * 4

img =3D bits_to_ndarray(bits, shape=3D(8, 8))
plt.imshow(img)
plt.show()


Oscar