Chapter 48: The Rise of Interleaved 2 of 5 (I2of5) |
Summary Snapshot |
This chapter explores Interleaved 2 of 5 (ITF), a numeric-only barcode symbology that emerged as a high-density alternative to Code 39 for applications where only digits are needed. By encoding data in pairs---with the first digit represented by bars and the second by the spaces between them---ITF achieves roughly double the density of Code 39 for numeric data. However, this efficiency came with trade-offs: the lack of alphanumeric support, the requirement for an even number of digits, and a somewhat lower theoretical data security compared to Code 39. This chapter examines the technical characteristics of ITF, its relationship to Code 39, and its widespread adoption across industries ranging from logistics and warehousing to retail and even entertainment media, explaining why each application chose this symbology and how its features shaped its use. |
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1. Introduction: The Need for a Denser Numeric Code |
The success of Code 39 in the 1970s and 1980s established barcodes as an essential tool for automatic identification and data capture across countless industries. Code 39's great strength was its ability to encode alphanumeric characters---the full uppercase alphabet, digits, and several special symbols---using a simple, self-checking pattern of wide and narrow bars and spaces. This versatility made it the 'workhorse' of early barcode adoption, appearing on everything from automotive parts to library books. |
Yet Code 39 had a significant drawback: its density. Every character in Code 39 is encoded using five bars and four spaces, with two of the five bars wide and one of the four spaces wide, plus an intercharacter gap between each character. This meant that a data string of, say, ten digits would require a relatively long barcode symbol. For applications that only needed to encode numeric data---such as product serial numbers, warehouse location codes, or shipping container identifiers---the alphanumeric capability of Code 39 was overkill, and the space required on labels and packaging became a limiting factor. |
In 1972, a solution emerged from the labs of Intermec Corporation, the same company that had brought Code 39 to the world. David Allais, the inventor of Code 39, turned his attention to creating a symbology that could pack numeric data into a much smaller footprint. The result was Interleaved 2 of 5, also known as ITF or I2of5 . This new symbology promised to encode numeric-only data in roughly half the space required by Code 39, opening up new possibilities for applications where space on labels, packaging, or products was at a premium . |
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2. How Interleaved 2 of 5 Works |
To appreciate why ITF achieved such a dramatic increase in density, it is helpful to understand its underlying architecture. |
The '2 of 5' Family |
Interleaved 2 of 5 belongs to a family of barcode symbologies known as the '2 of 5' codes. As the name suggests, each character in a 2 of 5 code is represented by a pattern of five elements---either bars or spaces---where exactly two of those five elements are wide and the remaining three are narrow. The specific pattern of wide and narrow elements determines which digit (0 through 9) is encoded . This is the same basic encoding principle used in Code 39, where each character also has two wide elements out of five, but Code 39 uses both bars and spaces within a single character along with an intercharacter gap. |
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Interleaving: Encoding in Pairs |
The 'Interleaved' part of the name is where the true innovation lies. Instead of encoding one digit at a time using a complete pattern of five bars and five spaces (as in Code 39), ITF encodes digits in pairs. The first digit of the pair is represented by the patterns of five bars, and the second digit is represented by the patterns of five spaces that fall between those bars. These bar and space patterns are interleaved with one another---hence the name 'Interleaved' 2 of 5 . |
For example, to encode the digits '12', the barcode would have ten elements total: five bars representing the digit '1' interleaved with five spaces representing the digit '2'. This interleaving eliminates the intercharacter gaps that take up space in Code 39, allowing the barcode to be significantly shorter for the same amount of data . |
The Start and Stop Patterns |
Like all linear barcodes, ITF requires start and stop patterns to tell the scanner where the barcode begins and ends. However, unlike Code 39 which uses an asterisk (*) as both the start and stop character, ITF uses different patterns at each end. The start pattern consists of four narrow elements: narrow bar, narrow space, narrow bar, and narrow space. The stop pattern consists of a wide bar, narrow space, and narrow bar . These distinct patterns help the scanner recognize the orientation and boundaries of the barcode. |
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An Even Number of Digits Required |
A direct consequence of the interleaving design is that ITF can only encode an even number of digits. Because the bars represent one digit and the spaces represent the next digit, each pair consumes one complete barcode symbol. If the data to be encoded has an odd number of digits, a leading zero must be added to make the number even. For instance, the number '12345' would be encoded as '012345' with a leading zero . Barcode printing software typically handles this automatically, adding a leading zero when needed. |
Optional Check Digit |
ITF supports an optional modulo 10 (Mod 10) check digit for error detection . This check digit is calculated using the same algorithm as the UPC barcode. When enabled, it provides an extra layer of data integrity, helping scanners detect misreads caused by printing defects, damage, or scanning errors. However, because the check digit adds one more digit to the data string, it requires an even total number of digits, which may necessitate an additional leading zero if the data plus check digit is odd . |
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Bearer Bars: A Unique Feature |
One of the most distinctive features of ITF barcodes, particularly in logistics applications, is the use of bearer bars. Bearer bars are thick horizontal or rectangular bars that surround the barcode symbol, often forming a complete frame around the data area . |
Bearer bars serve two important purposes. First, they address a practical challenge encountered when printing barcodes directly on corrugated cardboard boxes. When flexible rubber printing plates come into contact with the uneven surface of cardboard, they tend to bend, causing the printed barcode to become distorted. By adding bearer bars perpendicular to the data-expressing bars, box printers can stiffen the printing plates and produce a cleaner, more readable barcode . |
Second, bearer bars help prevent a scanning problem known as 'partial scan.' If a barcode reader passes over the barcode at too sharp an angle, it may fail to read the data-expressing bars at the ends of the symbol. Bearer bars help guide the scanner and ensure a complete read of the barcode. For these reasons, bearer bars are sometimes included even on ITF barcodes printed on plain labels . |
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3. Interleaved 2 of 5 vs. Code 39: A Technical Comparison |
To fully appreciate the role of Interleaved 2 of 5, it is useful to compare it directly to Code 39, the symbology it aimed to complement. |
Density |
The most significant advantage of ITF is its density. For purely numeric data, ITF achieves roughly twice the density of Code 39. BarTender's barcode documentation notes that 'barcode messages that only contain numbers can be encoded in Interleaved 2 of 5 using about half the space required by Code 39' . This means that a 10-digit numeric string that might require a 3-inch Code 39 barcode could fit in a 1.5-inch ITF barcode. |
This density advantage comes from the elimination of intercharacter gaps and the interleaving of bar and space patterns. On dot-matrix printers, the densest ITF barcodes can achieve about nine characters per inch, while laser printers can reach up to 17 characters per inch . |
Character Set |
Code 39 encodes the full uppercase alphabet (A-Z), digits (0-9), and several special characters, making it suitable for a wide range of alphanumeric data. ITF, on the other hand, only encodes digits (0-9) . This is its fundamental limitation and the reason it never replaced Code 39 entirely. When alphanumeric data is needed---such as part numbers containing letters or mixed identifiers---Code 39 remains the appropriate choice. |
Data Security |
ITF is considered to have slightly lower theoretical data security than Code 39. While ITF is self-checking (meaning that any single substitution error is detectable because it would violate the two-wide-out-of-five rule), it is more susceptible to certain types of errors. The BarTender documentation advises that 'the theoretical data security of Interleaved 2 of 5 is not quite as high' as Code 39, and recommends always using the optional check digit or standardizing on a fixed length to improve reliability . |
Encoding Rules |
Code 39 requires start and stop asterisks and has a fixed character encoding structure. ITF has the unique requirement of an even number of digits due to its interleaving design. This means that encoding '123' in Code 39 is straightforward, but in ITF it would become '0123' (adding a leading zero). Printing software handles this conversion, but users should be aware of the requirement . |
Applications |
Code 39 is highly versatile and appears in many industries---automotive, defense, healthcare, libraries, and more---where alphanumeric data is common. ITF is primarily used in logistics and warehousing, retail shipping, and other applications where only numbers are needed and label space is at a premium . |
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4. Applications of Interleaved 2 of 5 Across Industries |
Despite its limitations, Interleaved 2 of 5 found widespread adoption across numerous industries. Its density advantage made it particularly valuable in applications where large volumes of numeric data needed to be encoded in small spaces or where packaging materials posed printing challenges. |
Logistics and Warehousing |
The logistics and warehousing industry was the primary driver of ITF adoption. Since its invention by Intermec in 1972, ITF was initially used in warehousing and heavy industry . The ability to encode warehouse location codes, item numbers, and shipping identifiers in a compact barcode was invaluable for inventory management and order fulfillment. |
In a typical warehouse, thousands of products are stored in racks, bins, and pallets. Each location and each product requires a unique identifier that can be scanned quickly and reliably. ITF's high density allows more information to be placed on labels affixed to shelves, bins, or individual items without requiring oversized labels. Warehouse workers can scan ITF barcodes from a distance using handheld scanners, and the optional Mod 10 check digit helps ensure accuracy even in dusty or imperfect environments. |
By 1981, ITF was being used in the United States for transport packaging applications, and in 1987, Japan standardized the symbology for use in storage and distribution units . This international acceptance helped cement ITF's position as a logistics standard. |
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Shipping and Transport Packaging |
ITF is widely used on shipping cartons and transport packaging, where label space is often limited and the need for fast, accurate scanning is critical. In this context, the specific GS1-standardized variant called ITF-14 has become the dominant standard. ITF-14 is a 14-digit barcode used to encode Global Trade Item Numbers (GTINs) on cases, pallets, and shipping containers . |
The ITF-14 barcode is typically printed directly onto corrugated cardboard boxes using flexible printing plates. This is where bearer bars become essential---they prevent distortion during printing and ensure the barcode remains scannable despite the uneven surface of the cardboard . The ITF-14 barcode is sometimes called the 'box code' or 'shipping container code,' and it is a key component of the GS1 system for retail supply chains . |
A typical scenario involves products like cereal boxes, canned goods, or electronics that are individually labeled with UPC or EAN barcodes. When these individual items are packed into a shipping case or onto a pallet for transportation to a distribution center, the shipping container itself gets an ITF-14 barcode. This allows warehouse workers to scan the entire case or pallet without needing to scan every individual item, dramatically speeding up receiving, inventory, and shipping processes . |
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Retail and Consumer Goods |
In retail, ITF is used primarily at the case and shipping level rather than on individual consumer products. While individual items are usually labeled with UPC or EAN barcodes, the cases and pallets that contain multiple items are labeled with ITF-14 barcodes . This allows retailers to manage inventory at the case level, track shipments from suppliers, and streamline the replenishment of store shelves. |
When a pallet of merchandise arrives at a retail distribution center, the dock workers scan the ITF-14 barcode on the pallet. The system instantly knows the contents of the pallet---how many cases, what products, which lot numbers---and can direct the pallet to the appropriate storage location or store delivery route. This efficient process reduces handling time and errors, lowering supply chain costs. |
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Warehouse Sorting Systems |
Modern distribution centers often use automated conveyor systems that sort thousands of packages per hour based on information encoded in barcodes. ITF barcodes are well-suited for this environment because they are highly reliable and robust to printing variation. The barcodes are printed on shipping labels and read by high-speed laser scanners as packages move along the conveyor. The compact nature of ITF allows more barcode data to be placed within the limited space available on sorting labels, and the bearer bars help maintain readability even as packages bounce and shift on the conveyor. |
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Aviation Ticketing |
One of the more unusual applications of ITF is in aviation ticketing. The International Air Transport Association (IATA) adopted ITF for encoding ticket serial numbers and other numeric data on airline tickets . The original paper tickets had limited space for barcodes, and ITF's compact density allowed IATA to encode the required numeric data in a barcode that would fit on a ticket stub. |
These barcodes were used for ticket validation, baggage handling, and passenger tracking. An airline agent would scan the barcode on the ticket to verify the passenger's reservation, print boarding passes, and tag checked luggage with the correct destination. Although paper tickets have largely been replaced by electronic tickets (e-tickets), the legacy of ITF in aviation remains. |
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Film and Entertainment Media |
A surprising application of ITF is on 135 film cartridges, where ITF barcodes are used to encode film speed, roll number, and other data . The limited space available on the film canister and the need for a robust, easily scannable code made ITF a natural choice. |
When a photographer takes a roll of film to a photo lab for processing, the lab technicians scan the ITF barcode on the canister or film cartridge. This identifies the customer, associates the film with a specific order number, and may encode information about the film type. Even in the digital age, some film-based applications continue to use ITF. |
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Circular Interleaved 2 of 5 for Disc Media |
Building on the success of ITF, a circular variant of the symbology was developed specifically for labels used with disc-based media such as CDs, DVDs, and Blu-ray discs . This variant, known as Circular Interleaved 2 of 5, offers the same density advantages as ITF but is designed to be arranged in a circular pattern around the center of a disc. |
On a CD or DVD, the available space for a barcode is quite limited. The circular barcode is printed on the label side of the disc, near the inner hub or around the perimeter. This allows manufacturers to encode serial numbers, production dates, or inventory data directly on the disc without using valuable space that could otherwise be used for artwork or other content. The circular design also accommodates the physical constraints of disc manufacturing and labeling. |
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5. The Standardization of ITF |
As ITF gained acceptance in global supply chains, the need for formal standards became apparent. Standardization ensures that barcodes can be printed by one company and read by another without compatibility issues. |
ISO/IEC 16390 |
The international standard for ITF is ISO/IEC 16390, 'Information technology - Automatic identification and data capture techniques - Interleaved 2 of 5 bar code symbology specification' . This standard defines the symbology's technical specifications, including element widths, character encoding, and quality requirements. ISO/IEC 16390 ensures that ITF barcodes printed by different manufacturers in different countries can be consistently read by scanners from any vendor. |
GS1 and ITF-14 |
The GS1 organization, which develops and maintains the global standards for supply chain barcodes, has adopted ITF as the basis for ITF-14, the standard for encoding GTIN-14 numbers on shipping containers and transport packages . |
GS1 specifications require that ITF-14 barcodes have 14 data digits (including a check digit) and must use bearer bars to ensure printing quality on corrugated cardboard. The standard also specifies quiet zone requirements of at least 10 narrow bar widths around the barcode to prevent scanner interference from surrounding artwork or text . |
Other Variants |
There are several other variants and relatives of ITF. Standard 2 of 5 (also called Industrial 2 of 5) is a non-interleaved version that encodes each character separately but is less dense. Other 2 of 5 variants include IATA 2 of 5, Matrix 2 of 5, and DataLogic 2 of 5, each with minor variations in encoding rules or applications . However, ITF itself has remained the most widely adopted member of the 2 of 5 family. |
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6. Strengths and Weaknesses in Practice |
Strengths |
The primary strength of ITF is its high density for numeric data. In applications where only digits are needed, ITF can encode roughly twice as much data in the same space as Code 39 . This makes it ideal for labels with limited real estate, such as shipping labels, warehouse bin tags, and disc media. |
ITF also offers flexibility in printing. It can be printed at low resolution on dot-matrix printers or at high resolution on laser printers and flexographic presses. The symbology's two-width design (wide and narrow elements) makes it tolerant of variations in print quality, although proper bearer bars and quiet zones are essential for reliable scanning. |
ITF is recognized by virtually all barcode scanners on the market. Its widespread use in logistics and shipping has ensured that scanner manufacturers support ITF decoding. This universal compatibility simplifies adoption and integration into existing scanning systems. |
Weaknesses |
The most significant weakness of ITF is its numeric-only character set. Any application requiring letters, punctuation, or other non-numeric characters must use another symbology like Code 39 or Code 128 . |
ITF also has a lower theoretical data security than Code 39, making the optional Mod 10 check digit important for mission-critical applications . Without a check digit, ITF is more susceptible to substitution errors that can result in misread data. The check digit adds one digit to the barcode, reducing density slightly but significantly improving reliability. |
The requirement for an even number of digits is another practical consideration. Users must remember to add leading zeros when encoding odd-length numbers, although software handles this automatically in most cases. |
Bearer Bars: A Double-Edged Sword |
The bearer bars required for ITF-14 applications are both a strength and a potential weakness. While they prevent printing distortion and help scanners read the barcode, they also increase the physical footprint of the barcode and can be mistaken for part of the data if not properly positioned. The bearer bars must be printed carefully to ensure they do not interfere with the quiet zone or overlap with the data bars . |
Scanning Considerations |
ITF barcodes can be scanned from either direction due to the distinct start and stop patterns. However, because ITF is a continuous symbology without intercharacter gaps, it is more susceptible to 'short scan' errors where the scanner reads only part of the data before losing lock. Using a fixed length for all ITF barcodes or enabling the check digit can help prevent this problem . |
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7. Interleaved 2 of 5 in the Modern World |
A Complementary Symbology |
It is important to position ITF not as a replacement for Code 39 but as a complementary symbology that excels in specific niches. Code 39 remains the go-to for alphanumeric data, while ITF is the best choice for numeric-only, high-density applications. The two symbologies have coexisted peacefully for decades, each finding its natural home in different parts of the supply chain and beyond. |
Legacy and Current Status |
The legacy of ITF is significant. It was one of the first barcode symbologies to achieve widespread adoption in logistics, and it laid the groundwork for today's highly efficient supply chain infrastructure. ITF-14 remains the standard for case-level barcodes in retail, and shipping companies continue to rely on ITF for package tracking and sorting. |
While newer barcode symbologies like Code 128 offer even greater density and support more character sets, ITF persists because of its simplicity, reliability, and the installed base of equipment and processes that rely on it. In many warehouses, factories, and distribution centers, ITF barcodes are so common that they are taken for granted---invisible infrastructure that keeps goods moving. |
The Rise of 2D Barcodes |
The barcode landscape has evolved significantly since ITF's invention. Two-dimensional (2D) barcodes like Data Matrix, QR Code, and PDF417 offer much higher data capacity and can encode full alphanumeric data in a tiny area. 2D barcodes also have built-in error correction, making them extremely reliable even when damaged. |
However, 2D barcodes require higher-resolution printing and more sophisticated scanners, which can be a barrier in some applications. For simple numeric data in logistics, ITF remains a practical and cost-effective solution. It has proven remarkably resilient, continuing to serve industries that prioritize simplicity, cost-effectiveness, and compatibility. |
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8. Detailed Summary and Conclusion |
Interleaved 2 of 5 emerged in 1972 as a high-density numeric barcode symbology designed to complement Code 39. Its key innovation was interleaving---encoding the first digit of a pair in the bars and the second digit in the spaces between them. This eliminated intercharacter gaps and roughly doubled the data density for numeric information compared to Code 39. However, ITF's character set is limited to digits (0-9), and it requires an even number of characters. It offers an optional Mod 10 check digit for error detection and benefits from bearer bars that prevent printing distortion and improve scanning reliability. |
The technical characteristics of ITF directly shaped its applications. The high density made it ideal for compact labels in logistics and warehousing, where package tracking numbers and location codes had to fit in limited space on shipping labels or bin tags. The compatibility with corrugated cardboard printing, bolstered by bearer bars, made ITF-14 a standard for case-level shipping containers. The compact size enabled aviation ticketing applications where barcodes had to fit on paper ticket stubs. The circular variant extended the symbology to disc media like CDs, DVDs, and Blu-ray discs. |
ITF's limitations also defined its boundaries. The numeric-only character set meant it could not replace Code 39 for alphanumeric data---a role that Code 39 still excels in. The lower theoretical data security required the use of check digits in critical applications. The need for an even number of digits demanded careful data formatting and awareness from users. |
Compared to Code 39, ITF offers roughly double the density for numeric data, but lacks alphanumeric support and has a slightly higher risk of misread errors. ITF is more specialized, while Code 39 remains the more general-purpose symbology. Both symbologies have coexisted since the 1970s, each carving out its own niche in the vast ecosystem of automatic identification. |
The standardization of ITF under ISO/IEC 16390 and the adoption of ITF-14 by GS1 have ensured global interoperability and long-term viability. While 2D barcodes continue to gain prominence, ITF remains a reliable and cost-effective choice for numeric data in logistics, shipping, and related fields. Its legacy lives on in the billions of shipping labels, warehouse bin tags, and cardboard cartons that pass through the global supply chain every day. |
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In the larger story of barcode symbology, Interleaved 2 of 5 stands as a testament to the power of clever engineering---a focused solution to a specific problem that has become an indispensable part of modern commerce and logistics. It reminds us that sometimes the most impactful innovations are those that do one thing exceptionally well, even if that one thing is simply making numbers smaller. |
cs@easiersoft.com