Barcodes are also called bar codes. Bar code was first proposed by NT. American woodland 1949. With the popularization of computer application, the application of bar code has been greatly developed. Barcode can indicate the country of production, manufacturer, commodity name, date of production, book classification number, starting and ending place, category and mailing date, so it has been widely used in many fields such as commodity circulation, book management, post and telecommunications management, banking system and so on. Bar code is composed of bars and spaces with different widths and reflectivity, which is compiled according to certain coding rules (coding system) and is used to represent a group of graphic identifiers of digital or alphabetic symbol information. That is, bar code is a group of parallel lines with different thicknesses and arranged at certain intervals. Common bar codes are composed of black bars (referred to as bars) and white bars (referred to as spaces) with great differences in reflectivity.

In order to read the information represented by bar code, a bar code recognition system is needed, which consists of bar code scanner, amplification and shaping circuit, decoding interface circuit and computer system.

Bar codes are applied to printers. Bar code printers use traditional printing methods. Bar code printer is a kind of printing equipment that can quickly print a large number of self-adhesive labels, pet labels, tags, washed cloth and so on. Generally, there are two ways of thermal transfer and thermal transfer, using special label paper and carbon tape. Barcode printers should be selected where a large number of labels need to be printed, especially where factories need to print a large number of labels in a short time, and where special labels (such as PVC materials and waterproof materials) need to be printed immediately (such as ticket offices). If you often print a lot of labels or have special requirements for labels, please choose to use a barcode printer. Bar code printers have been widely used in all aspects of production and life, such as supermarkets, government departments, manufacturing enterprises, logistics and so on.

Bar code classification: one-dimensional and two-dimensional bar codes.

Because the information capacity of one-dimensional bar code is very small, the application scope of bar code is limited to some extent. Then came the two-dimensional bar code. In addition to the advantages of ordinary bar code, two-dimensional bar code also has the advantages of large information capacity, high reliability, strong security and anti-counterfeiting, easy manufacture and low cost. 199 1 year, American Symbol company officially launched a two-dimensional code named PDF4 17, referred to as "portable data file". FDF4 17 two-dimensional barcode is a portable data file with high density and high information content, and it is an ideal means to realize automatic storage, carrying and reading of large-capacity and high-reliability information such as certificates and cards.