Frequently Asked Questions : Bar Code Technology FAQs : Mechanics

What are the elements of a bar code?

No matter which symbology you will be using, all bar code share elements that make up the symbol. These are the bars and spaces, the human readables, and the quiet zone. In addition, a symbology may be either Discrete or Continuous.

Bars and Spaces

The bars and spaces determine the pattern of the encoded data. Each symbology represents a different strategy behind the creation of these patterns such as: being as condense as possible, printing as easily as possible, being as easy to decipher as quickly as possible, etc.

Each bar code has slightly different quiet zone requirements. For example, the quiet zone of Code 39 is ten times the width of the thinnest bar/space or 0.25 inches, whichever is greater.

Human-Readables

The human-readable is the data represented by the bars and spaces printed as text for people to read. The actual data encoded here is 3*35353*2. The asterisks are not displayed as human-readables in this example.

The Quiet Zone

The quiet zone is the clear area (free from marks) before and after the bars and spaces. Having a quiet zone is as important to readability as the bars and spaces! Scanners need to establish values for the quiet zone before they can evaluate the bars and spaces. Reading the color and reflectance of the quiet zone establishes how the spaces will read and determines the difference between the spaces and the bars. Bar code cannot be read without a quiet zone.

Bar Code Pro will generate at least the minimum required quiet zone for each particular code. Even though the quiet zone actually surrounds the code (the Bar/Space image), the clear area above and the below the Bar/Space image is not required for readability of most symbologies.

Discrete vs. Continuous bar code

Discrete symbologies consist of unique bar and space patterns for each character. Continuous codes cannot be separated into individual characters.

ITF is a continuous bar code. You cannot pull it apart into discrete, individual characters. Notice how the bars of the 3 and 5 are embedded in the bars of the 8 and 2.

Codabar is a discrete bar code. You can pull apart characters into discrete, individual units. The spaces between characters do not have critical dimensions.

The pattern of the number five is 310000102 where å11 is a wide bar or space and å01 is a narrow bar or space.

Updated: 05/12/2003