Read QR code from image file with Python (Mac)

Use ZBar and the Python module https://pypi.python.org/pypi/zbar/. It also supports barcodes other than QR codes.

In order to streamline the aggregation of experimental results using paper cards, I made a note that I prepared a QR code in the card in advance and automatically processed it with Python after scanning.

Environment, version

Mac OS X (10.9 Mavericks) & Homebrew
ZBar 0.10 http://zbar.sourceforge.net/
Python zbar 0.10
Python Pillow (Python Imaging Library) 2.7.0

Installation

ZBar

One-shot installation with Homebrew.

$ brew install zbar

Python zbar module

I'd like to install this with PyPI in one shot, but if I put it in as it is, Python will die with a Segmentation fault at the time of import.

$ pip install zbar

$ python
Python 2.7.9 (default, Jan  7 2015, 11:50:42) 
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.56)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import zbar
Segmentation fault: 11

$ pip uninstall zbar

Stack Overflow: Zbar + python, crashes on import (OSX 10.9.1)

Therefore, apply Patch to the source code and install it. In this patch, we add sentinel to the array to prevent the occurrence of Segmantation fault.

$ wget https://pypi.python.org/packages/source/z/zbar/zbar-0.10.tar.bz2
$ wget https://github.com/npinchot/zbar/commit/d3c1611ad2411fbdc3e79eb96ca704a63d30ae69.diff
$ tar jxvf zbar-0.10.tar.bz2
$ cd zbar-0.10
$ patch -p1 < ../d3c1611ad2411fbdc3e79eb96ca704a63d30ae69.diff
patching file imagescanner.c
$ python setup.py install

$ python
Python 2.7.9 (default, Jan  7 2015, 11:50:42) 
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.56)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import zlib
>>>

This time it was okay.

Python Pillow module

Enter with one PyPI.

$ pip install Pillow

Extract the QR code from the image file

Python test code.

zbar_test.py

`zbar_test.py`


#!/usr/bin/env python
# -*- coding: utf-8 -*-

### cf. http://99blues.dyndns.org/blog/2010/12/zbar/

import sys
import zbar
import PIL.Image
 
if len(sys.argv) < 2: exit(1)
 
# create a reader
scanner = zbar.ImageScanner()
 
# configure the reader
scanner.parse_config('enable')
 
# obtain image data
pil = PIL.Image.open(sys.argv[1]).convert('L')
(width, height) = pil.size
raw = pil.tostring()
 
# wrap image data
image = zbar.Image(width, height, 'Y800', raw)
 
# scan the image for barcodes
scanner.scan(image)
 
# extract results
for symbol in image:
    # do something useful with results
    print 'decoded', symbol.type, 'symbol', '"%s"' % symbol.data
 
# clean up
del(image)

$ ./zbar_test.py /path/to/image.jpg
decoded QRCODE symbol "http://www.example.com/"