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Guide to decoding barcodes

Cognex UK : 12 September, 2013  (Technical Article)
Cognes has published a paper explaining the different types of barcode, their application and how to read them.
Guide to decoding barcodes
Barcode technologies provide fast reliable data collection to ensure part or product traceability, error-proof assembly processes, and enhance customer service.
Barcodes are machine readable symbols that store identifying data about the part or product with which they are associated. These symbols, when read by a barcode scanner, are decoded, recorded, and processed to extract the data for a variety of uses (e.g., pricing, order fulfillment, traceability through production, sortation, shipping, etc.)
Over the years, different forms of barcodes have been developed to help businesses around the world.
It might be hard to remember a time when barcodes were not part of our daily lives, but it was not until the 1970s that they first made an impact. Although the first patent was actually issued in 1952, it was still some time later that they were commercially used to label railroad cars.
However, it took until June 1974 before the first scanner was installed at a Marsh’s supermarket in Ohio, USA, allowing a product with a barcode attached to be read for the very first time. Unassumingly, this was just a simple packet of Wrigley’s chewing gum.
Decades after that first scan, we can hardly imagine a world without barcodes. Available in various guises, barcodes continue to benefit industries that manufacture, buy, sell and distribute products. They help collect data faster and more reliably, improve decision making, eliminate the possibility of human error, reduce employee training time and track
products throughout their lifecycle. They are also extremely versatile, inexpensive to design and print and ultimately reduce costs.
1-D linear barcodes
1-D linear barcodes are probably the most commonly recognized style of barcode used today. The following selection of symbols help illustrate their multiple forms:
Code 128
Code 128 is a more recently introduced symbol and the most robust 1-D barcode type. The number 128 refers to the ability to hold any character of the ASCII 128 character set. That includes all digits, characters and punctuation marks. This makes it fairly compact and very powerful as it enables diverse storage of data.
By far the most common and well-known barcode used in the US, UPC-A encodes 12 digits of data. The first digit is the number system character followed by a five-digit manufacturer number, a five-digit product number and a final check digit. Due to its limited encoding, UPC-A is primarily used in retail.
EAN-13 is the European counterpart of the UPC-A symbol. The main difference between them is that the EAN-13 encodes an extra digit of data to make a total of 13. The first two digits of the barcode identify a specific country and the check digit is the last number of the second group of six digits.
UPC-E is a condensed variation of a UPC-A barcode. The code is condensed as a result of eliminating ‘extra’ zeros from the digital data. Because the resulting barcode is about half the size of a UPC-A barcode, it is generally used on very small packaging where space is limited.
EAN-8 is the EAN equivalent of UPC-E in the sense that it provides a short barcode. Set in two groups of four numbers, it is composed of two flag digits, five data digits and one check digit. This is primarily used on small packaging where space is limited.
Code 39
Code 39, also known as ‘3 of 9 Code’, was the first symbol to use numbers and letters. It is a variable-length barcode that is self-checking so a check digit normally isn’t necessary, but is recommended. Its popularity is due to its ability to encode up to 43 numbers, letters and other characters. Code 39 is still widely used, especially in non-retail environments.
Extended Code 39
Extended Code 39 uses a combination of two standard Code 39 characters to encode every one of the 128 ASCII characters. It also allows for special characters, such as lowercase letters. Generally, the more special characters that are used, the longer the barcode will become. Most barcode readers will not automatically read Extended Code 39 without custom configuration.
Code 93
Code 93 was designed to encode data more compactly and with higher data redundancy than with older multi-length barcode types such as Code 39.
Codabar is a discrete, self-checking barcode that allows encoding of up to 16 different characters, plus an additional four special start and stop characters, which include A, B, C and D.
Interleaved 2 of 5
Interleaved 2 of 5 encodes any even number of numeric characters. Unlike Standard 2 of 5 (a.k.a. Industrial 2 of 5), which only encodes information in the width of the bars, Interleaved 2 of 5 encodes data in the width of both the bars and spaces. This allows Interleaved 2 of 5 to achieve higher density encoding.
MSI/Plessey, also known as Modified Plessey, is used primarily to mark supermarket shelves for inventory control. MSI is a continuous, non-self-checking barcode. While the barcode can be of any length, a given application usually implements a fixed-length barcode.
GS1 DataBar Omnidirectional
GS1 DataBar Omnidirectional barcodes are self-checking, high data density codes. Designed to hold the 14 digits of the GTIN (Global Trade Item Number), it is smaller than the UPC and EAN barcodes making it excellent for use on smaller items like produce. It can also be stacked or combined with other codes to create composite codes.
GS1 DataBar Expanded
GS1 DataBar Expanded barcodes were designed to encode Application Identifiers, allowing a greater range of data to be encoded such as expiry date, weight, and batch number. Again, these can also be stacked or combined with other codes to create composite ones.
Postal codes
Over the years nearly every country in the world has developed their own postal codes to best suit their needs. However, in recent times there has been a move towards standardizing them. This type of barcode lies somewhere in between a 2-D and a 1-D linear barcode. Instead of encoding data in the black bar and white space widths, these primarily use the height of the bars. The majority of postal codes only use numbers, but a few are now starting to include letters as well.
The POSTNET (Postal Numeric Encoding Technique) barcode is used by the US Postal Service to automatically sort mail. Unlike most other barcodes in which data is encoded in the width of the bars and spaces, POSTNET actually encodes data in the height of the bars.
Intelligent Mail Barcode
The IMB (Intelligent Mail Barcode) is a US Postal Service barcode used to sort and track letters and flats. In addition to the ZIP code used to generate a POSTNET barcode, the IMB carries sender’s information.
2-D matrix codes
In the 2-D (two-dimensional) matrix code type, the data is encoded as black and white ‘cells’ (small squares), arranged in either a square or rectangular pattern. As well as being able to encode huge amounts of data, the matrix code improves readability and resistance to poor printing. They also include redundant data so even if one or more cells are damaged, the code is still readable.
Data Matrix
Data Matrix codes allow encoding of large amounts of data (up to 2,335 alphanumeric or 3,116 numerical characters) and use an error correction system to read codes that are as much as 40% damaged. They are made up of black and white cells in a square or rectangular pattern, a finder pattern and a timing pattern.
MaxiCode is a fixed-size code which holds up to 93 data characters. It is composed of a central bulls-eye locator and offset rows of hexagonal elements. It was created by United Parcel Service to allow quick, automated scanning of packages on high-speed conveyor lines (high powered image-based barcode readers can read a MaxiCode on a carton travelling at up to 168 m/min).
QR (Quick Read) codes contain square blocks of black cells on a white background with finder patterns in the top left, top right, and bottom left corners. QR was developed with the intention of being used for tracking parts during vehicle assembly. However, it has grown in popularity since the introduction of readers on smartphones, and it is now
commonly used in printed marketing materials.
Named after the resemblance of the central finder pattern to an Aztec pyramid, the code is built on a square grid with a bulls-eye pattern at its center for locating the code. Data is encoded in concentric square rings around the bulls-eye pattern. Aztec codes have the potential to use less space than other matrix barcodes because they do not require a surrounding blank ‘quiet zone’.
Stacked linear barcodes
A stacked linear barcode is another type of 2-D barcode. These simply consist of multiple linear barcodes that are layered on top of one another, allowing a greater amount information to be encoded. However, to fully decode the data, a barcode reader must be able to simultaneously read the code both horizontally and vertically.
GS1 DataBar Stacked
GS1 DataBar Stacked barcodes are designed to condense the GTIN into a more compact and square barcode suitable for use on smaller packages (such as the label stickers on fresh produce).
PDF417 barcodes can store up to 1800 printable ASCII characters or 1100 binary characters per symbol. It is also possible to break large amounts of data into several PDF417 codes which are linked together. In theory, there is no limit to the amount of data that can be stored in a group of PDF417 symbols.
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