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====== Introduction ======
The goal of this program is to detect and decipher one or several QR codes in a picture.

====== Required Libraries ======
In order to decipher QR codes, we will use the zbarlight library, installed (on Debian) as follows:\\
''apt-get install libzbar0 libzbar-dev''\\
''pip install zbarlight''\\
We will also use a number of standard Python libraries.

<code python>
 from PIL import Image
 import zbarlight
 from subprocess import Popen, PIPE
 import sys
 import datetime
</code>

====== Explanation =====
The program allows exactly one argument: the IP address of the Raspberry Pi whose camera we're going to be using.\\
To avoid any issue, we check that it is a valid IP address with the following function:
<code python>
 def isValidIPV4(adr):
   nums = adr.split('.')
   if len(nums) != 4:
       return False
   try:
       return all(0 <= int(num) < 256 for num in nums)
   except ValueError:
       return False
</code>

If the right argument was given, we can remote into the pi to take a picture. To do so, we use subprocess.Popen() to run the following command with the given ip:\\
''ssh -t pi@<ip> "raspistill -hf -vf -o <nom_fichier> --nopreview --timeout 10"''\\
To avoid conflict with an already existing picture, we put the date and time in the new picture's name.

<code python>
 if (len(sys.argv) == 2 and isValidIPV4(sys.argv[1])):
    filename = 'qrcodereader_' + datetime.datetime.now().strftime("%Y-%m-%d-%H:%M:%S") + '.jpg'

    print("Taking picture...")
    command = ['ssh', '-t', 'pi@' + sys.argv[1], "raspistill -hf -vf -o " + filename + " --nopreview --timeout 10"]
    x = Popen(command, stdout=PIPE, stderr=PIPE)
    stderr = x.stderr.read()
    print stderr
</code>

We then import the resulting image over ssh using the ''rsync'' command.

<code python>
    print("Importing...")
    command = ['rsync', '-avz', '--ignore-existing', '--remove-source-files', 'pi@' + sys.argv[1] + ':~/' + filename, '/home/silver/BE/' + filename]
    x = Popen(command, stdout=PIPE, stderr=PIPE)
    stderr = x.stderr.read()
    print stderr
</code>

We now simply use zbarlight to decode any and all QR codes fully visible on the picture. We only need to open and load the image, before applying the scan_codes function.

<code python>
    file_path = './' + filename
    with open(file_path, 'rb') as image_file:
        image = Image.open(image_file)
        image.load()
    
    code = zbarlight.scan_codes('qrcode', image)
    print('QR codes: %s' % code)
</code>

The program outputs a full list of all deciphered QR codes.