Bar codes
Bar codes are visual representations of information designed for decoding by optical scanners known as bar code readers. These codes consist of a series of dark and light bars, which correspond to a unique sequence of numbers and letters. The concept of bar codes originated in the late 1940s when two graduate students aimed to automate the checkout process in supermarkets, leading to the first patent for an optical reading device. Although initial prototypes faced challenges, advances in technology during the 1960s, including lasers and integrated circuits, made practical bar code readers possible.
Today, bar codes are widely utilized across various industries, primarily in retail to streamline product tracking and sales transactions. Their applications extend beyond retail to include patient identification, airline luggage management, and document management. Bar codes are structured with specific zones that facilitate accurate reading, including quiet zones, character chains, and checksums for error verification. Notably, bar code readers can interpret codes of various sizes, a feature known as scale invariance, making them versatile tools in modern technology.
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Bar codes
Summary: Bar codes encode numerical data visually for product identification and other purposes.
A bar code is a visual representation of information intended to be decoded by an optical scanner called a bar code reader. The reader illuminates the bar code, thus allowing its light sensor to detect the patterns of dark and light bars. The sequence and width of dark and light bars represents a unique sequence of numbers and letters.
Origins
It took 26 years for the idea of bar codes to be successfully implemented in the retail industry. In 1948, two graduate students at Drexel University, Norman J. Woodland and Bernard Silver, overheard a conversation in which the president of a local supermarket chain in Philadelphia wished to automate the checkout process. At that time, a cashier in a supermarket would have to type into a cash register the price of all items in a purchase—a time-consuming and error-prone task. Woodland and Silver filed a patent application in 1949, obtaining the patent in 1952, for an optical device that would read information automatically. The first prototype was produced by IBM but was impractical because of both its size and the heat generated by the 500-watt light bulb used by the bar code scanner. The patent was sold in 1952 to the Philadelphia Storage Battery Company (Philco), which was also unable to produce a viable prototype, and sold the patent the same year to the Radio Corporation of America (RCA). Bernard Silver died in a 1963 car accident, before the bar code system was implemented in practical settings. The invention of lasers and integrated circuits in the 1960s allowed the manufacture of small, low-energy bar code readers. RCA developed a modern version of bar codes in 1972 in a Kroger store in Cincinnati, but the code was printed in small stripes that were easily erased or blurred by employees who had to attach them manually to each item. Norman J. Woodland was an employee at IBM at the time and led a team that produced bar codes according to a standard known as Universal Product Code (UPC) still in use today. Bar codes are used in nearly all retail products worldwide. The applications of bar codes have also reached far beyond the retail industry; they are now used in such disparate applications as patient identification, airline luggage management, and document management, as well as purchase receipts.
The Mathematics of Bar Codes
The most ubiquitous form of bar codes consists of a visual pattern of long lines (hence the “bar” in “bar code”), which has four well-defined zones (see Figure 1): (1) quiet zone, or empty zone, located in the left and right zones of the code; (2) initial character (right) and final character (left) are standard bars that appear on all bar codes, and indicate where the information begins and ends; (3) variable-length character chain, which contains as many characters as needed to encode the message; and (4) checksum, which is a number that is computed algebraically from the other characters using modular arithmetic, and is used to verify that the characters have been correctly transmitted and interpreted. The digits are either simply added or are weighted. For example, the 10-digit International Standard Book Number (ISBN-10) uses weights based on digit position and modulus 11 arithmetic.
Each digit is encoded by two white and two black bars. The bars have widths of 1 to 4 units, and the total width for each digit is always seven units. Bar code readers are designed to read bar codes irrespective of their size; a magnified bar code encodes the same information as a reduced-size bar code. This property is mathematically known as scale invariance.
Bibliography
Adams, Russ, and Joyce Lane. The Black & White Solution: Bar Code & the IBM PC. Dublin, NH: Helmers Publishing, 1987.
Palmer, Roger C. The Bar Code Book: A Comprehensive Guide to Reading, Printing, Specifying, Evaluating, and Using Bar Code and Other Machine-Readable Symbols. 5th ed. Victoria, BC: Trafford Publishing, 2007.
Wittman, Todd. “Lost in the Supermarket: Decoding Blurry Bar codes.” SIAM News 37, no. 7 (September 2004).