Barcodes are vital to imaging. They help you get organized. They help you track your work. They save you time. Printing them well is important. Reading them quickly is vital.
Unlike most printing applications, it's vitally important to print your barcodes accurately and precisely. Most barcodes rely on the relative thickness of the bars and spaces to encode their data. If the barcode is even slightly distorted, it's difficult to read. This slows down processing.
Keep in mind the resolution of your printer. The lower your printer's resolution, the less dense the barcode must be to be readable. For most formats, 300 dpi is the lowest resolution. Most laser and ink jet printers do better than 300 dpi so this shouldn't be a problem. Code 39 and Postnet can be printed on low resolution dot matrix printers. The most challenging output device for barcodes is the fax machine.
If you are planning to fax a barcode, take special precautions to ensure it will be readable. Select a barcode that will perform well at low resolutions. Code 39 is a good choice. Standard fax resolution is 203 x 98 dpi.
Fine mode is 203 x 196. Fax in fine mode. Position the barcode so that the lines are at right angles to the high resolution direction. This gives you the best resolution across the width of the bars. Fax directly from a computer file whenever possible.
Print the barcode as large as possible -- especially if you expect the barcode to be returned by fax -- it will be scanned at the same low resolution twice. Don't trust a barcode's appearance on a computer screen. Video displays are about 72 dpi -- too poor to show most barcodes clearly. It's very difficult to judge whether a barcode is printed properly just by looking at it.
It's a good idea to verify a barcode's print quality with a barcode verifier when it's printed. A verifier measures the barcode, checks if it meets the format's specifications. Synex (Brooklyn, NY 718-499-6293) offers a barcode verifying service. They also sell verifying devices starting at $900.
Checking barcode print quality is especially important when printing a large number of barcoded documents or mailing labels. Print gain is when printers slightly enlarge printed items. It's not important when printing text or pictures, but it's critical with barcodes. Narrow bars gain much more width as a percentage of their size than wide bars.
Most barcodes rely on the proportional differences between bars and white spaces. Because print gain increases the size of all the bars by a fixed (non-proportional) amount, it can throw your barcode reader. A high-resolution printer can reduce print gain. Bar width reduction software lets you apply reverse print gain. This corrects the problem.
If the barcode format permits checksum characters, use them. Checksum character are determined when a barcode is printed. All the characters in the barcode are added and a mathematical calculation is performed to determined the checksum.
When the barcode is read back, the mathematical operation is performed again. The result is compared to the checksum. The data in damaged barcodes can frequently be reconstructed based on the checksum. Checksum characters provide an extra level of security. This can save you hours of typing redundant information. Check digits are required with many barcode formats.
Finally, when printing barcodes, bear in mind the method in which they'll be scanned. Specialized barcode scanners, whether hand held or fixed, have a fairly high resolution, often more than 1,000 dpi. They will scan a barcode hundred of times per second and are optimized to read barcodes. Document scanners don't have half the resolution of a barcode scanner. If you want to scan barcoded documents on a document scanner, make sure the barcode is large enough to be read efficiently.
Reading Barcodes
Document imaging systems normally have barcode reading incorporated into the scanning and OCR software. There are also a number of standalone products. Most barcode reading software works with databases and specialized data entry applications. Specialized barcode scanners provide higher resolution than the flatbed scanners. A barcode reader must have sufficient resolution to read the finest barcode found in an application. It only needs to scan in black and white. Even when barcodes are relatively small, as long as they conform to barcode standards, they can be read very quickly. This permits barcode scanners that operate fast enough to be hand held.
Contact Scanners. These scanners look like heavy pens. Barcodes are read by pressing the tip of the scanner up against the barcode and drawing it across the bars. This type of scanner only reads one-dimensional barcodes. It's slow because the operator must manually scan the barcode. The barcodes must be printed on a material sturdy enough to be scanned repeatedly.
Contact scanners are portable and measure according to their aperture. The aperture is the smallest feature that can be scanned. A scanner with a 10 millimeter aperture reads barcodes with bars larger than 10/1000ths of an inch. It's important to match the scanner's aperture to the resolution of the barcode you're scanning. Theoretically, a scanner with an aperture of, say six millimeters can read barcode whose thinnest bar is 15 millimeters. In practice, large, low resolution barcodes have voids that can fool a small aperture scanner.
Non-Contact Scanners. Handheld types of non-contact barcode scanners look like a gun with a short wide barrel. Non-contact scanners fall into two categories. Laser scanners use a laser beam to "see" the barcode. Although expensive, laser scanners are fast high resolution devices that scan barcodes at distances up to 35 feet.
Charge Coupled Device (CCD) scanners use a row of light emitting diodes to light up the barcode. A CCD camera scans the barcode. CCD scanners are a little slower than laser scanners. They're a lot cheaper. Often half the cost of a laser scanner. Their range is quite short. Just a few inches. CCD scanners are good for point of sale applications.
Non-contact scanners are often used in CD and tape jukeboxes to read barcoded volume numbers. Non-contact scanners are also used in fixed installations. A typical application are supermarket scanners. Permanently installed scanners can be highly automated. In enterprise-based document management systems, barcodes are frequently read from scanned images. A document is read by a scanner in preparation for storage, optical character recognition, or handwriting recognition.
The scanning software is designed to recognize barcodes embedded in the documents and to funnel the them to an interpreter. Barcodes are also used on separator sheets between bundles of documents about to be scanned.
Remember document scanners don't have the resolution of barcode scanners. A barcode scanner has an effective resolution of more than 1,000 dpi and will scan a barcode up to 40 times per second. A document scanner, especially a high speed scanner, will read the barcode just once at 200 dots per inch. When using document scanners, make sure the barcodes are printed large and clear enough for the software to recognize them.
Any step that can be made to improve barcode recognition should be taken. That includes the adding check digits and printing the barcodes on high-contrast paper at the best resolution. With two dimensional barcodes experts suggest a special procedure to scan barcodes such as PDF-417. Scan two dimensional barcodes in grayscale.
Once the barcode is decoded, the document can be converted to black and white for on-line storage. Grayscale scanning improves the readability of two dimension barcodes on 200 dpi scanners.
