Encoding of the Code 39 barcode involves specific rules and patterns to represent alphanumeric characters, special symbols, and control characters. Code 39, also known as USD-3, 3 of 9, or Alpha39, is a widely used linear barcode symbology that can encode uppercase letters (A-Z), digits (0-9), and a set of special characters (-, ., $, /, +, %, and space). This encoding system utilizes a series of bars and spaces varying in width to represent each character. Let's delve into the details of how characters are encoded in Code 39. |
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Character Set and Structure |
1.Character Set: Code 39 can encode the following characters: Uppercase letters (A-Z) Digits (0-9) Special characters (-, ., $, /, +, %) Space character ( ) |
2.Start/Stop Characters: Code 39 uses asterisks (*) as start and stop characters. These are not part of the data but are used to denote the beginning and end of the barcode. |
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Encoding Rules |
1.Basic Encoding: Each character in Code 39 is represented by a pattern of nine elements (five bars and four spaces), where each element can be wide or narrow. A narrow element is typically one unit wide, and a wide element is two to three units wide. 2.Character Mapping: Each character corresponds to a specific pattern of bars and spaces. For example, the letter 'A' is represented by the pattern of bars and spaces that uniquely identifies it as 'A' in the Code 39 specification. 3.Character Patterns: The encoding of characters in Code 39 is based on a series of bars (dark bars) and spaces (light spaces). The width of each element (bar or space) and the sequence of these elements determine which character is represented. |
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Example Encoding |
Let's encode the string 'CODE39' using Code 39 encoding: |
1.Start Character: Every Code 39 barcode begins and ends with an asterisk (). Thus, our barcode starts with ''. |
2.Character Conversion: C: Encoded as '1101010010110' O: Encoded as '1101001010110' D: Encoded as '1011001010110' E: Encoded as '110101100110' 3: Encoded as '1011011010010' 9: Encoded as '1010110110010' |
3.Check Character: Code 39 includes a modulo-43 checksum character for error detection. It is optional but often used for ensuring accuracy in barcode scanning. |
4.Stop Character: The barcode ends with another asterisk (*). |
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Detailed Steps for Encoding: |
Start with the asterisk (*) character. Convert each character ('C', 'O', 'D', 'E', '3', '9') into its corresponding pattern of bars and spaces. Concatenate these patterns together to form the complete barcode. Optionally, calculate and append the checksum character for enhanced reliability. |
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Character Mapping Table |
Here's a simplified mapping table for some characters in Code 39: |
CharacterPattern |
A1010011011010 B1101001010110 C1011001010110 ...... 01010011011010 11101001010110 21011001010110 ...... *1010110010100 -1010110010100 .1010110010100 $1010110010100 /1010110010100 +1010110010100 %1010110010100 (space)1010110010100 |
Example Barcode Construction |
Given the string 'CODE39': |
Start Character: '*' Encode each character using its respective pattern. Combine all encoded patterns together. Optionally, calculate and append the checksum character. End Character: '*' |
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Conclusion |
Encoding in Code 39 involves converting each character into a unique pattern of bars and spaces. These patterns are then concatenated to form the complete barcode. Each character has a specific representation defined by the Code 39 standard, ensuring consistent and accurate scanning across different systems. Understanding these encoding rules is crucial for generating and interpreting Code 39 barcodes effectively in various applications such as inventory management, shipping, and document tracking. |
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