The format and structure of a barcode

A barcode consists of a series of thick and thin alternating vertical dark and light bars of different widths which are printed on to labels and packaging

A barcode quite simply consists of a series of thick and thin alternating vertical dark and light bars of different widths which are printed on to labels and packaging used for retail, industrial, business and commercial applications and which can be automatically read to provide a fast, accurate and efficient method of collecting and recording data.

The concept behind a barcode is actually quite simple. Every item that you want to code or classify is given its own unique number in a barcode format, which is then printed onto the label or pack, and can subsequently be electronically scanned so that the coded information can be read.

Figure 2.1 - Barcodes consist of alternating thick and thin vertical dark and light bars

The dark and light spaces in the barcode represent digitally encoded information, which can be ‘read’ by devices (barcode readers and barcode scanners), which scan a beam of light across the bars and so pick up signals from the various pulses of reflected light. The dark bars in the code absorb light while the white spaces reflect light, so providing a cost-effective method for automating data collection.

It would be possible to print a number without coding it, but numbers alone can be easily confused when they are electronically read . for example, six is identical to nine when turned upside down and will not therefore give the correct number if scanned the wrong way up.

What is therefore needed is a reliable method of coding so that the coded information can be reliably read from any direction, at high speed if necessary, each and every time. This is where the black and white lines come in. Each digit in, say, a retail barcode number is given an equal amount of space consisting of 7 units, or 7 equal-sized vertical blocks, which are colored with a different pattern of black and white stripes that then represent the decimal numbers from zero to nine.

This can be seen in Figure 2.2.

Figure 2.2 - How barcodes can be used to represent the numbers from zero to nine

To read successfully, a barcode symbol requires a light, blank margin or clear area on the left and right sides of the barcode or possibly surrounding the bar code symbol. This area is called the ‘Quiet Zone’.

The quiet zone is a compulsory requirement in barcode generation. Scanners need them in order to read the barcode bars.

To ensure that barcodes will scan first time and meet their acceptance requirements it is normally Picket fence orientation necessary to have some kind of quality control device. When used in conjunction with the printing of barcodes these devices are called verifiers.

Verifiers check that the barcode matches the specifications within the permitted tolerance levels, as well as confirming that the bars and spaces correctly correspond to the human readable information.

Codes used in the label and related industries can be found in a wide variety of types and formats and are used in applications as diverse as warehousing, storage, shipping, asset tracking, security printing, cheque reading, point-of-sale, authenticity, inventory control, product and parts identification, stock taking and other areas.

Barcodes used in the label and packaging industry can be found in a number of different formats. Some barcodes represent numbers only . as can be found in the EAN and UPC retail barcodes, UPC shipping container codes and in Interleaved 2 of 5 codes (ITF).

These codes are known as ‘Numeric’ codes (see Figure 2.5).