activePDF Toolkit 2011 API Reference
Barcode Terminology
Appendices > Barcode Terminology

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This section is designed to provide an overview of the common terminology used to define barcode formats. These terms include:


Character Set—Character Set refers to what data a given barcode symbology can encode. Generally, there are three types of character sets:

  • Numeric—The symbology can encode only numeric data from 0 through 9. Some additional characters may be encoded, which are generally control features of the symbology, such as start/stop characters.
  • Alphanumeric—The symbology can encode the digits 0 through 9 as well as alphabetic characters from A through Z. Some additional characters may be encoded, which are generally control features of the symbology, such as start/stop characters.
  • Full ASCII—The symbology allows the encoding of the full ASCII character set. This symbology encodes any ASCII character, value 0 through 127.

In general, a numeric character set produces the smallest barcode, whereas a Full ASCII character set requires a larger space to encode the same data. However, Full ASCII provides increased flexibility in encoding more types of information.

Label Area—Label area describes the entire symbol, including the symbol margins, the barcode, the human readable text, the comment and comment margins. The label area does not include the label border.

Symbol Margins—The symbol margins define the area between the label border and the area composed of the barcode, human readable text, comment and comment margins.

Barcode—The barcode is the symbol you scan. This does not include the human readable text, except when the human readable text is required in the barcode.

Human Readable Text—Human readable text is the displayed barcode value. This can be the actual barcode value or a numerical representation and can appear above or below the barcode. Visible human readable text invalidates certain barcodes.

Comment —A comment is additional text displayed with the barcode, but not included in the encoded value. Comments appear above or below the barcode, within the label area. You can place comment text above or below the barcode and define separate comment margins.

Comment Margins—Comment margins are the defined area around the comment text. The comment margins are determined in relation to the type and size of barcode. 

Label Border—The label border is the perimeter of the label area. Changes in the label border should not affect the label area or barcode. 

Discrete—In a discrete symbology, the interpretation of each character encoded does not rely on the rest of the barcode. Such symbologies have characters that both start and end with a bar. Some amount of inter-character spacing or inter-character gap separates each character. The inter-character gap carries no information-the only duty of the inter-character spacing is to separate the characters.

Continuous—In a continuous symbology, the interpretation of each character encoded relies on the rest of the barcode. This is because characters start with a bar and end with a space. The final space is "terminated" by the starting bar of the next character. Individually, there is no way to know how wide the last space is without knowing where the next character begins. Continuous symbologies normally implement some kind of special termination bar or, the termination bar is such that the last space of the last data character terminates termination sequence.

Width—There are two different width symbologies:

  • Two-Width symbology—has spaces and bars that are either wide or narrow. This has the benefit of simplicity, as once the width of a narrow bar is determined, anything over a certain width is "wide". This allows for a large level of print tolerance in lower-quality printing conditions.
  • Multiple-Width symbology—has bars and spaces that may be of three or more widths. The narrowest bar or space may be X in width, a medium-width space or bar may be 2X in width, and a wide bar may be 3X in width. Since there are more possible combinations available in a multiple-width symbology, data encoding is often more efficient and results in a tighter barcode. Multiple-width symbologies are usually continuous.

Length—There are two length symbologies:

  • Fixed-length symbology—encodes a certain number of characters or digits. For example, a UPC-A barcode always encodes 12 digits of data. An application may not encode less or more than the predefined fixed-length of 12 characters. The symbology itself defines the length of data.
  • Variable-length symbology—encodes a message of any length. For example, Code128 encodes any number of characters that can reasonably fit physically in the printed barcode. The symbology itself does not define how many characters to encode.  

Self-Checking—A self-checking symbology means a single printing or scanning error will not cause one of the component characters to convert into another valid character.  NOTE: Self-checking does not infer self-correcting.

Element—An element is any individual bar or space.

Module—A module is the amount of space a bar or space takes up measured in X's. For example, a narrow bar is 1X, thus the narrow bar takes up one module. A medium-size bar may be 2X in width, thus it would take up two modules. A wide bar may be 3X in width, thus it takes up three modules.

Character—A character is a sequence of elements (bars and spaces) which, taken together, encode a single logical value. Often, each character in a barcode is a fixed number of modules in length.

Density—Density is the number of characters encoded per inch given a certain X value. The smaller the X value, the more characters encoded in an inch of a barcode. 

Value X—The value "X" is the "perfect" width of the barcode's narrowest element. The value of X must remain constant throughout a single barcode.