pylibdmtx

Read and write Data Matrix barcodes from Python 2 and 3 using the libdmtx library.

• Pure python
• Works with PIL / Pillow images, OpenCV / imageio / numpy ndarrays, and raw bytes
• Decodes locations of barcodes
• No dependencies, other than the libdmtx library itself
• Tested on Python 2.7, and Python 3.5 to 3.10

The older pydmtx package is stuck in Python 2.x-land.

Installation

The libdmtx DLLs are included with the Windows Python wheels. On other operating systems, you will need to install the libdmtx shared library.

Mac OS X:

brew install libdmtx

Linux:

sudo apt-get install libdmtx0a

The PyPI package is currently out-of-date; to install the latest version, use:

pip install git+https://github.com/NaturalHistoryMuseum/pylibdmtx.git

To use the read_datamatrix and write_datamatrix command-line scripts, you will also need to install Pillow >= 3.2.0:

pip install "Pillow>=3.2.0"

If you want to install the outdated package from PyPI:

pip install pylibdmtx
pip install pylibdmtx[scripts]

Example usage

The decode function accepts instances of PIL.Image.

>>> from pylibdmtx.pylibdmtx import decode
>>> from PIL import Image
>>> decode(Image.open('pylibdmtx/tests/datamatrix.png'))
[Decoded(data='Stegosaurus', rect=Rect(left=5, top=6, width=96, height=95)),
 Decoded(data='Plesiosaurus', rect=Rect(left=298, top=6, width=95, height=95))]

It also accepts instances of numpy.ndarray, which might come from loading images using OpenCV.

>>> import cv2
>>> decode(cv2.imread('pylibdmtx/tests/datamatrix.png'))
[Decoded(data='Stegosaurus', rect=Rect(left=5, top=6, width=96, height=95)),
 Decoded(data='Plesiosaurus', rect=Rect(left=298, top=6, width=95, height=95))]

You can also provide a tuple (pixels, width, height)

>>> image = cv2.imread('pylibdmtx/tests/datamatrix.png')
>>> height, width = image.shape[:2]
>>> decode((image.tobytes(), width, height))
[Decoded(data='Stegosaurus', rect=Rect(left=5, top=6, width=96, height=95)),
 Decoded(data='Plesiosaurus', rect=Rect(left=298, top=6, width=95, height=95))]

The encode function generates an image containing a Data Matrix barcode:

>>> from pylibdmtx.pylibdmtx import encode
>>> encoded = encode('hello world'.encode('utf8'))
>>> img = Image.frombytes('RGB', (encoded.width, encoded.height), encoded.pixels)
>>> img.save('dmtx.png')
>>> print(decode(Image.open('dmtx.png')))
[Decoded(data=b'hello world', rect=Rect(left=9, top=10, width=80, height=79))]

Windows error message

If you see an ugly ImportError when importing pylibdmtx on Windows you will most likely need the Visual C++ Redistributable Packages for Visual Studio 2013. Install vcredist_x64.exe if using 64-bit Python, vcredist_x86.exe if using 32-bit Python.

Limitations

Feel free to submit a PR to address any of these.

• I took the bone-headed approach of copying the logic in pydmtx’s decode function (in pydmtxmodule.c); there might be more of libdmtx’s functionality that could usefully be exposed
• I exposed the bare minimum of functions, defines, enums and typedefs neede to reimplement pydmtx’s decode function

Contributors

• Vinicius Kursancew (@kursancew) - first implementation of barcode writing
• Joseph Weston (@jbweston) - support for libdmtx 0.7.5

License

pylibdmtx is distributed under the MIT license (see LICENCE.txt). The libdmtx shared library is distributed under the Simplified BSD license (see libdmtx-LICENCE.txt).