A barcode is a really simple idea: give every item that you want to classify its own, unique number and then simply print the number on the item so an electronic scanning device can read it. We could simply print the number itself, but the trouble with decimal numbers is that they're easy to confuse (a misprinted eight could look like a three to a computer, while six is identical to nine if you turn it upside down—which could cause all sorts of chaos at the checkout if you scanned your cornflakes the wrong way up). What we really need is a completely reliable way of printing numbers so that they can be read very accurately at high speeds. That's the problem that barcodes solve.
Photo: Each digit in a barcode is represented by seven equal-sized vertical blocks. These are colored in either black or white to represent the decimal numbers 0–9. Every number ultimately consists of four fat or thin black and white stripes and its pattern is designed so that, even if you turn it upside down, it can't be confused with any other number.
If you look at a barcode, you probably can't make head or tail of it: you don't know where one number ends and another one begins. But it's simple really. Each digit in the product number is given the same amount of horizontal space: exactly 7 units. Then, to represent any of the numbers from zero through nine, we simply color those seven units with a different pattern of black and white stripes. Thus, the number one is represented by coloring in two white stripes, two black stripes, two white stripes, and one black stripe, while the number two is represented by two white stripes, one black stripe, two white stripes, and two final black stripes.
You've probably noticed that barcodes can be quite long and that's because they have to represent three different types of information. The first part of a barcode tells you the country where it was issued. The next part reveals the manufacturer of the product. The final part of the barcode identifies the product itself. Different types of the same basic product (for example, four-packs of Coca-Cola bottles and six-packs of Coca-Cola cans) have totally different barcode numbers.
Most products carry a simple barcode known as the UPC (universal product code)—a line of vertical stripes with a set of numbers printed underneath it (so someone can manually key in the product number if the barcode is misprinted or damaged in the store and won't scan through the barcode reader). There is another kind of barcode that is becoming increasingly common and its stores much more information. It's called a 2D (two-dimensional) barcode) and you sometimes see it on things like self-printed postage stamps.
Photo: Two sets of very thin "guard bars" (which I've indicated in red) show where a barcode begins and ends, while a third set in the middle separates the product code (yellow) into two chunks of data (0028 and 1003 in this example). The guard bars make it easier for the scanner to detect a barcode, figure out which way up it is, and help to identify it when it's blurred (more about this down below).
It would be no good having barcodes if we didn't have the technology to read them. Barcode scanners have to be able to read the black-and-white zebra lines on products extremely quickly and feed that information to a computer or checkout terminal, which can identify them immediately using a product database. Here's how they do it.
For the sake of this simple example, let's assume that barcodes are simple on-off, binary patterns with each black line corresponding to a one and each white line a zero. (We've already seen that real barcodes are more sophisticated than this, but let's keep things simple.)
In some scanners, there's a single photoelectric cell and, as you move the scanner head past the product (or the product past the scanner head), the cell detects each part of the black-white barcode in turn. In more sophisticated scanners, there's a whole line of photoelectric cells and the entire code is detected in one go.
One major complication here is that the barcode (or the scanner) is often moving during the scanning process (think how you swipe items at a self-serve grocery checkout) or it might be so far from the scanner that the code is out of focus. That means the pattern the scanner produces is not a crisp set of easy-to-identify black and white stripes, but a blurred smudge made of more ambiguous grey shades. Various different computer algorithms can be used to turn these blurred patterns into accurate barcodes, including edge-detection, which looks for sudden changes in brightness where a zero gives way to a one, or vice-versa. If you want to know exactly how these algorithms work, check out the technical references at the end of this article.
Photo: Left: Barcodes as we see and think of them are clear and crisp zebra patterns. Middle: Barcodes as scanners capture them may be smudged beyond recognition. Right: Using edge-detection and other algorithms, it's possible to turn blurred images back into something like a usable barcode.
Photo: A typical wand-type barcode scanner (also called a barcode reader). Readers like this are usually wired to computers or checkouts and contain little or no computing power. Photo by Naoto Anazawa courtesy of US Air Force and DVIDS.
Different types of barcode scanners are available for all kinds of applications. In small, convenience stores, you'll typically find a basic wand scanner. The simplest ones look like electronic pens or giant, oversized razors. They shine red LED light onto the black and white barcode pattern and then read the pattern of reflected light with a light-sensitive CCD or a string of photoelectric cells. If you have a pen scanner, you have to run it across the barcode so it can reach each block of black or white in turn; with a wand scanner, the CCD or photocells read the entire code at once.
Photo: Scanning a barcode with Amazon's iPhone/iPod app. You find a product you like, scan the code, and the online store pops up with the product details automatically.
In a busy superstore, you're more likely to see a very sophisticated laser scanner. It'll be built into the base of the checkout lane, under a piece of glass, and you may be able to see the laser beam being bounced around at high-speed by a spinning wheel so it reads products (literally) in a flash. Another technology uses a small video camera to take an instant digital photograph of the barcode. A computer then analyzes the photograph, picking out only the barcode part of it and converting the pattern of black and white bars into a number. (Barcode-scanning apps that run on cellphones work this way, using the phone's built-in camera to photograph the code.) Scanners like this can accurately read dozens of products waved past them each minute and are far more accurate than old-style checkouts (where you have to key in the price of every item by hand). The best barcode scanners are so accurate that they make only one mistake in something like 70 million pieces of scanned information! (Compare that to typing on a keypad, where you're typically likely to make one error in every 100 characters you type.)
Photo: A handheld computer with built-in barcode scanner. Unlike a simple wand-type scanner, this one can store and process data from the objects it scans, which can be uploaded to a computer later on using WiFi, Bluetooth, or the built-in cellphone connection. Photo by Taylor L. Jackson courtesy of US Navy and DVIDS.
Barcode scanning technology has been around since the early 1970s but only really caught on in the 1980s and 1990s after stores started to invest in sophisticated, computerized electronic point-of-sale (EPOS) checkout terminals. Back then, store checkouts cost many thousands of dollars. Today, scanners are much more affordable. You can buy a simple, USB barcode scanner and software and hook it up to an ordinary laptop or computer for just a few dollars. Thanks to barcodes, even tiny convenience stores can run as smoothly as Wal-Mart these days!
How did we arrive at a point where virtually everything we buy is marked with a barcode? Here are some of the key moments in barcode history:
Bernard Silver
(1924–1963) andN. Joseph Woodland
(1921–) get the idea for developing grocery checkouts that can automatically scan products. Woodland tries various different marking systems, including lines and circles, marks inspired by movie soundtracks, and dots and dashes based on Morse code. In October 1949, the two inventors refine their system to use bullseye patterns and apply for a patent (US Patent #2,612,944), which is granted on October 7, 1952. Their early barcode-scanning equipment uses a conventional lamp to illuminate product labels and a photomultiplier (a crude type of photoelectric cell) to read the light reflected off them. In 1951, Joe Woodland joins IBM to work on barcode technology, though the company declines to purchase his patent, which is acquired by Philco (and later RCA).Artwork: The original barcodes didn't use "zebra" stripes, like they do today, but "bullseye" patterns like these. Artwork from US Patent #2,612,944: Classifying apparatus and method by Woodland and Silver, courtesy of US Patent and Trademark Office.
Alan Haberman
(1929–2011), executive vice president of First National Stores in Boston, the stores come together to form the Uniform Code Council (UCC), later known as GS1 US, the organization that now manages barcode standards worldwide.I've dipped into the archives of the US Patent and Trademark Office and pulled out the records of the original barcode pattern scanner, invented by N. Joseph Woodland and Bernard Silver. I've colored and numbered it to quickly illustrate how it worked. In the top picture, you can see the entire apparatus, including the barcode scanner, which is shown in the center in blue; in the lower picture, you can see a more detailed view of the scanner itself:
Artwork courtesy of US Patent and Trademark Office. You can find a full description and more detailed drawings in US Patent #2,612,944: Classifying apparatus and method by Norman J Woodland and Bernard Silver.
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