Decoding Bar Codes

EVERY product that comes with a UPC

code (Universal Product Code) or barcode

is scanned and decoded to reveal

information about it at the time of its

purchase. A barcode can be scanned

through the use of various technologies

like laser scanners, CCD (Charge Coupled

Device) readers and camera based

readers.

Each UPC symbol has two parts viz.

the machine-readable bar code and the

human-readable 12-digit UPC number.

The first six digits are manufacturer

identification numbers whereas the last

five digits are the product numbers.

In the image below we see that 639382

are manufacturer numbers whereas

00039 are the product numbers. The UPC

Co-ordinator, is responsible for assigning

product numbers while making sure that

same codes are not assigned to other

products.

The last digit on a UPC code is called

a check digit. This digit helps the scanner

check whether it scanned the digit

correctly. We now see how the check digit

is calculated for the other 11 digits on the UPC. We use the

image below as an

example.

First you will

have to add all

digits placed in

odd positions i.e.

6 + 9 + 8 + 0 + 0

+ 9 = 32

Multiply the

number by 3, i.e.

32 * 3 = 96

Now, add all

digits placed in

even positions i.e. 3 + 3 + 2 + 0 + 3 = 11

Add this sum to the value in step 2 i.e.

96 + 11 = 107

You will now have to add a number

to the result in step 4 such that the

number is a multiple of 10. For example

107 + 3 = 110.

Therefore 3 is the check digit.

Whenever a scanner scans a product,

the same calculation is performed. If

the check digit calculated differs from

the check digit it read, the scanner will

assume that something went wrong and

the product will be rescanned.

BAR CODE READERS

THE latest bar codes readers which are

used in grocery stores to decode product

bar codes are camera based. These

readers use a tiny video camera that

captures an image of the bar code.

The video camera used in a bar

code reader device has hundreds of

rows of sensors that arranged in a two

dimensional array to generate an image.

Once the image has been captured, the

reading device will use a digital image

processing technique to decode the bar code and find out the product id and its

assigned price.

The laser based bar code readers

generally use light sensors to measure

the intensity of the digital bar code that

it scans through. These readers are lined

with small yet powerful sensors, which

generate voltage on the bases of the

intensity of the bar code being scanned.

To create a readable bar code, the print

contrast between dark and light bars

should be adequate. Also the bar code

should have sharp bar edges, less spots

and smooth surface to make it readable.