Hardware Reference
In-Depth Information
Figure 9-4
A one-dimensional
barcode. This is the ISBN
bar code for this topic.
Barcode Recognition
A barcode is simply a pattern of dark and light lines or cells
used to encode an alphanumeric string. A computer reads
a barcode by scanning the image and interpreting the
widths of the light and dark bands as zeroes or ones. This
scanning can be done using a camera or a single photodi-
ode, if the barcode can be passed over the photodiode at a
constant speed. Many handheld barcode scanners work by
having the user run a wand with an LED and a photodiode
in the tip over the barcode, and reading the pattern of light
and dark that the photodiode detects.
to write a more comprehensive piece of software that
can interpret several symbologies, or you have to know
which one you're reading in advance. There are numerous
software libraries for generating barcodes and several
barcode fonts for printing the more popular symbologies.
Barcodes, such as the one shown in Figure 9-4, are called
one-dimensional barcodes because the scanner or camera
needs to read the image only along one axis. There are
also two-dimensional barcodes that encode data in a
two-dimensional matrix for more information density.
As with one-dimensional barcodes, there are a variety of
symbologies. Figure 9-5 shows a typical two-dimensional
barcode. This type of code, the QR (Quick Response)
code, was created in Japan and originally used for tracking
vehicle parts, but it's since become popular for all kinds of
product labeling. The inclusion of software to read these
tags on many camera phones in Japan has made the tags
more popular. The following project uses an open source
Java library to read QR codes in Processing.
The best known barcode application is the Universal
Product Code , or UPC , used by nearly every major manu-
facturer on the planet to label goods. There are many
dozen different barcode symbologies, which are used
for a wide range of applications. For example, the U.S.
Postal Service uses POSTNET to automate mail sorting.
European Article Numbering (EAN) and Japanese Article
Numbering (JAN) are supersets of the UPC system
developed to facilitate the international exchange of goods.
Each symbology represents a different mapping of bars to
characters. The symbologies are not interchangeable, so
you can't properly interpret a POSTNET barcode if you're
using an EAN interpreter. This means that either you have
ConQwest, designed for Qwest Wireless in 2003, by Area/Code
www.areacodeinc.com
The first ever use of Semacode, 2D barcodes scanned by phonecams. A
city-wide treasure hunt designed for high-school students, players went
through the city “shooting treasure” with Qwest phonecams and moving their
totem pieces to capture territory. A website tracked the players' locations and
game progress, turning it into a spectacular audience-facing event.
Photo courtesy of Area/Code and Kevin Slavin.
 
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