Barcode is constitute by plurality of black bars and blank, the width of black bars are different, and these bars arranged in encoding rules for expression a group of information, graphics and identifier. It usually appears in our lives asbarcode labels.

A common barcode is composed by black stripes (referred as articles) and white bars(referred as blank) which have a great difference in reflectance. The producing country of items, maker, product’s name, date of production, book CLC, mail starting and ending location, category or other information can be marked by it. So it has a wide range of applications in commodity circulation, library management, postal management, banking system and so on.

May be barcode labels seems very simple just like many black lines printed on a paper, but the recognition principle of barcode is not simple. The barcode need to be complied according to certain rules so that can be change into meaningful information. In order to get the information, it is need two steeps, scanning and decoding.

As white object can reflect the various wavelengths of visible light, the black object can absorbs various wavelengths of various wavelengths, when the light source send out light, reflected on the barcode, the light incident into the barcode scanner’s photoelectric conversion device, and according the different strength of the reflected light signal, barcode can be converted into a corresponding electrical signal.

Because the widths of articles and blank are different, the electrical signal corresponding duration length also different.

Then the digital electric signal 0,1 and numbers of bar and blank discriminated by measuring pulse of decoder, by measuring the duration of 0,1 to discriminate the width of bars and blank.

According the corresponding coding rules, with data processing and management, detailed information of item could be identified. That is the recognition principle inside barcode labels.