Smoky Cogs

The EAN-8 barcode format is a compressed format of the EAN-13 barcode, only containing 7 digits plus one checksum digit, and is generally used in places where a fullsized EAN-13 barcode would not fit.

To calculate the parity, we use the same process as with the EAN-13 barcode. We first need add up the 7 digits of the barcode with the weighting applied. For the EAN-7 barcode, the weighting of each digit which is in an odd-numbered position is 1 and for even-numbered positions, the weighting is 3. To find the sum, we need to multiply each digit by its weighting before adding it together.

Once we have the weighted sum, we apply a modulo 10 to the weighted sum, which gets the remainder after applying a modulo of 10 to the weighted sum.

The parity is then 10 – (modulo 10 of the weighted sum).

Now that we have an 8 digit number, we can encode it.

Like EAN-13, we split up the 8 digits we need to print into two blocks of 4 with a guard bar at the beginning and end of the barcode and one in the middle of the barcode too. The end guard bars are encoded as 101, while the middle guard bar is 01010.

The main difference now is that the parity digit is included in the barcode itself, rather than used to change the encoding, so it is remarkably simpler to implement.

For first 4 digits (the left hand side of the barcode) are encoded with the following encoding, which are the same as the odd parity encodings for the left hand side of EAN-13:

0	0001101
1	0011001
2	0010011
3	0111101
4	0100011
5	0110001
6	0101111
7	0111011
8	0110111
9	0001011

The right hand side encodings (the last 4 digits) are the same as the right hand codings of EAN-13.
The encodings are as follows:

0	1110010
1	1100110
2	1101100
3	1000010
4	1011100
5	1001110
6	1010000
7	1000100
8	1001000
9	1110100

continue reading…

The EAN-13 barcode format is the standard barcode used on everyday products across the world, except in the US, where the UPC-A barcode is more popular.

The EAN-13 barcode is a 13 digit barcode, where the first two or three digies are the country code where the manufacturer of the product is registered. The next nine or ten digits are data digits, which adds up to 12 digits. The last digit is the checksum digit.

To calculate the checksum (also known as the parity), we first need add up the 12 digits of the barcode with the weighting applied. For the EAN-13 barcode, the weighting of each digit which is in an odd-numbered position is 1 and for even-numbered positions, the weighting is 3. To find the sum, we need to multiply each digit by its weighting before adding it together.

Once we have the weighted sum, we apply a modulo 10 to the weighted sum, which gets the remainder after applying a modulo of 10 to the weighted sum.

The parity is then 10 – (modulo 10 of the weighted sum).

Now that we have a 13 digit number, we can encode the data we need to print out a barcode. Each digit is represented by a series of bars and spaces. I will represent a bar as 1 and a space as 0 for the rest of the tutorial.

EAN-13 splits up the 12 digits we need to print into two blocks of 6 with a guard bar at the beginning and end of the barcode and one in the middle of the barcode too. The end guard bars are encoded as 101, while the middle guard bar is 01010.

The parity of the barcode is not printed directly, but is rather used to determine which set of encodings we are going to use for each character, which complicates the encoding of the barcode slightly.

For first 6 digits (the left hand side of the barcode) there is an odd and even encoding. The parity defines which encoding to use. The parity check has a 6 digit binary string, where each digit determines whether to use the odd or even encoding set at the position in the parity string. So for example, for a parity of 3, the binary string is 110001, which means that at position 2, we need to use the odd set, and at position 3 we need to use the even set, and so on.

The parity encodings are as follows:

0	111111
1	110100
2	110010
3	110001
4	101100
5	100110
6	100011
7	101010
8	101001
9	100101

For the left hand side encodings then, the encodings are as follows:

Digit	Odd	Even
0	0001101	0100111
1	0011001	0110011
2	0010011	0011011
3	0111101	0100001
4	0100011	0011101
5	0110001	0111001
6	0101111	0000101
7	0111011	0010001
8	0110111	0001001
9	0001011	0010111

The right hand side encodings (the last 6 digits) do not need this and are just encode straight.
The encodings are as follows:

0	1110010
1	1100110
2	1101100
3	1000010
4	1011100
5	1001110
6	1010000
7	1000100
8	1001000
9	1110100

continue reading…

There are dozens of different standards when it comes to barcodes, and each of them has their own rules as to how they are worked out.

Some of them have checksum digits worked in. Some have parity, whereby alternate digits used different sets of data to output the bars, some work on fixed sized data, whereas others are variable, but they all have one thing in common.

They all are made up of a sequence of bars and spaces, where, based on the rules of the barcode being used, a digit is represented by a particular set of bars and spaces.

Here is the source for an application I have written in C# which calculates the encoding for various barcode formats and outputs the resulting barcode as an image.

The program currently encodes EAN-13, EAN-8, UPC-A, UPC-E, UPC-2, UPC-5, MSI, Postnet, Standard 2 of 5 and Interleaved 2 of 5. The most commonly found barcodes are the EAN-13 and UPC-A barcodes which are commonly found on most household goods.

I will cover the algorithms used to create each barcode in future blog posts, but for now, enjoy playing around with this app