By Jenny Hughart, BarTender® technical writer
A barcode is a type of automatic identification and data capture (AIDC) technology that consists of a series of parallel, adjacent bars and spaces (in the case of linear symbologies), dots and squares (in the case of two-dimensional [2-D] symbologies), or a combination of these (in the case of composite symbologies). The technology enables real-time data to be collected accurately and rapidly. AIDC technology creates the potential for improving performance, productivity, consumer safety, and efficiency in industries worldwide.
Code versus symbol versus symbology
The term "code" refers to the actual data that is contained in the arrangement of lines and spaces or squares and spaces. This data can be nearly anything: part number, manufacturer ID, transaction code, location code, expiration date, and so on. Data can be numeric, alphabetic, or alphanumeric. The encoded data can be used by a computer to look up additional information about the item in a database, such as price and description.
The term "symbol" refers to the physical elements that encode the data: the lines and spaces or squares (or dots) and spaces.
The term "symbology" refers to the rules by which the data is encoded into the physical elements of the symbol. Sometimes, the same data can be captured by different symbols, and choices must be made about which symbology fits the users' needs best. Depending on the symbology and application, users may be able to customize everything from the size and color of a barcode symbol to its industry function.
Components that are common to most barcode symbols include:
- X dimension: Specifies the width of the narrowest unit in a barcode. Usually, this is the width of the narrowest bar or space. A single X dimension is called a "module." Wider elements in the barcode are measured as multiples of the X dimension. Therefore, the X dimension correlates directly with the overall width of the barcode and therefore its density.
- Ratio: Specifies the ratio between the widths of the wide and narrow elements in a barcode.
- Density: Specifies the width of the bars and spaces in the barcode and defines how many characters can be encoded per inch.
- Height: Specifies the height of the barcode.
How barcodes work
Barcodes are read either by scanning a point of light across the symbol (as with a laser beam) and measuring its elements (bars and spaces) or by capturing an image of the symbol (as with a smartphone camera) and analyzing the pattern of its elements (squares and spaces). The reader analyzes the symbol elements, and the data is extracted.
What a barcode contains
Barcodes can contain different kinds of information, depending on which symbology is used. Many linear barcodes, such as UPC or Code 128, function as catalog numbers that are linked to a database that contains the descriptive data about the product. For example, the UPC barcode on a cereal box at a grocery store is linked to the store's database, and that database contains comprehensive information such as the manufacturer's name, product type, lot number, price, size, and so on.
Some linear barcodes and most 2-D barcodes can encode text, such as letters, numbers, and special characters. For example, a barcode on an ID badge may encode an employee's name and identification number.
Some 2-D barcodes are complex enough to contain thousands of characters' worth of information and can encode URLs, advertising, Short Message Service (SMS) messages, location information, and so on. Some codes were developed specifically to encode Chinese and Japanese characters.
Most barcodes include a check digit to ensure data integrity and to provide error correction. Additionally, most symbols must be surrounded by empty space, called the "quiet zone," in order to be scanned correctly.