Libdmtx

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Data Matrix is a format, like QR codes, for encoding data as a two dimensional graphical barcode. libdmtx is the free C library with support for creating and decoding. Bindings for other languages, including Python, exist.

Using libdmtx from the commandline

Installation

sudo apt-get install libdmtx-utils

Results in:

p   libdmtx-dev                                            - Data Matrix barcodes (development files and static libraries)    
i   libdmtx-utils                                          - Utilities for reading and writing Data Matrix 2D barcodes        
i A libdmtx0a                                              - Data Matrix barcodes (runtime library)

Encoding a message

Created a message in a text file (osv.txt), and then:

dmtxwrite osv.txt -o osv.png

Decoding a message

Decoding directly from the encoded image:

dmtxread osv.png

This time, the image is opened in the gimp, scaled it up, and photographed with a camera phone, then:

dmtxread IMG_20110906_150252.jpg -N1

The same message is decoded!

Decoding messages from a number of images

Display all messages from files ending with "jpg" in the current directory:

dmtxread -N1 -n -m1000 *.jpg

Parameters explained:

• -N1 : stop after 1 code (per image)
• -n : print a new line after each message
• -m1000 : limits search to 1000ms per image (give up if no message is found)

Using libdmtx from Python

Installing the Python bindings

sudo apt-get install libdmtx-dev
cd /usr/share/doc/libdmtx-dev/examples/python
# unzip the source files!
sudo gunzip pydmtx.py.gz
sudo gunzip pydmtxmodule.c.gz 
sudo python setup.py install

Decoding messages

From the Python interface code, the accepted keyword arguments (to just the decode function?):

*kwlist[] = { "width", "height", "data", "gap_size", "max_count", "context", "timeout", "shape", "deviation", "threshold", "shrink", "corrections", "min_edge", "max_edge" };

from pydmtx import DataMatrix
from PIL import Image
import sys
 
dm_read = DataMatrix()
for f in sys.argv[1:]:
    try:
        img = Image.open(f)
        result = dm_read.decode(img.size[0], img.size[1], buffer(img.tostring()), timeout=1000, max_count=1)
        print f, result
    except IOError:
        print "Bad image (IOError):", f