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Given the following text description, write Python code to implement the functionality described below step by step
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Description:
 Writing binary images with pillow
Pillow is a fork of PIL.
It's a useful image manipulation tool, but it seems to have some bugs when reading or writing binary data.
This Python notebook is to serve as a guide to working around issues in pillow.
Step1:  Here's the image, admittedly its small
Step2:  Here's the new image
Step3:  To write a binary file you first need to convert binary data to uint8 datatype and cast to that data type as well.
Then you need to convert using the Image.convert(mode) method to binary before saving.
Step4:  Writing direct to zipfiles
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Python Code:
#For data manipulations
%pylab inline
from IPython.display import set_matplotlib_formats
from io import BytesIO
import numpy as np
#to compare to scipy's builtin conversions
from scipy.misc import imsave, toimage
#import pillow
from PIL import Image
set_cmap('Greys')
checkerboard = np.mod(np.arange(49).reshape(7,7),2).astype('bool')
matshow(checkerboard)
#whats the dtype?
checkerboard.dtype
#create a PIL image with binary mode
cb_img = Image.fromarray(checkerboard,mode='1')
#write the image
cb_img.save('cb_img.bmp')
Explanation: Writing binary images with pillow
Pillow is a fork of PIL.
It's a useful image manipulation tool, but it seems to have some bugs when reading or writing binary data.
This Python notebook is to serve as a guide to working around issues in pillow.
End of explanation
#read in the image
cb_img_read = Image.open('cb_img.bmp')
#convert to array
checkerboard_read = np.asarray(cb_img_read)
#display 
matshow(checkerboard_read)
cb_img2 = Image.fromarray((checkerboard*255).astype('uint8'),mode='L')
#write the image
cb_img2.convert('1').save('cb_img2.bmp')
Explanation: Here's the image, admittedly its small:
but you can see there's no white!
End of explanation
a = array([True, False])
(a*255).dtype
#read in the image
cb_img2_read = Image.open('cb_img2.bmp')
#convert to array
checkerboard2_read = np.asarray(cb_img2_read)
#display 
matshow(checkerboard2_read)
Explanation: Here's the new image:
Now its a checkerboard!
End of explanation
checkerboard2_read.dtype
cb_img2.save()
Explanation: To write a binary file you first need to convert binary data to uint8 datatype and cast to that data type as well.
Then you need to convert using the Image.convert(mode) method to binary before saving.
End of explanation
import zipfile as zp
# this is admittedly not the most transferable
with zp.ZipFile("junk.zip","w") as zf:
    # generate an output byte buffer to save the data in, instead of a file
    output = BytesIO()
    # convert and save the image to the byte buffer with the correct format
    cb_img2.convert('1').save(output, "BMP")
    # wrtie the byte buffer to the zipfile directly
    zf.writestr("junk.bmp", output.getvalue())
Explanation: Writing direct to zipfiles
End of explanation
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