Understanding Barcodes (Part 2)

Salzman, Michael

Many Options in Design and Placement

How large should the symbol be?

The size of a barcode symbol has a lot to do with its ability to survive the perils of handling and scanning. But how big is big enough? Very large symbols are unsightly and can consume valuable space on a document. What size is too small? Too small symbols, even if they are quite visible on the form, lead to low recognition rates. Some users think that if a hand-held scanner (like those in retail stores) can read the symbol, then it's a good symbol. They don't realize that these hand-held scanners are totally different than recognition from scanned images. What's more, printing 1D symbols as fonts misleads users into thinking that if a 10 or 12 point font is good enough for the text, then it should be good for the barcode as well.

The correct answers depend on what is to be done with the barcode document. Will it be printed once and scanned? Or faxed? Or faxed and printed and faxed back? Will it be scanned at 200dpi or 300dpi? Furthermore, the answer depends on how much data is included, the shape of the space available for the barcode, the handling of the document and several other aspects.

Most applications require a more careful design performed in conjunction with expert assistance. However, the rule of thumb answer for simple applications such as cover pages, or for separator pages, is to assume that the document will be scanned at 200dpi. Barcodes are measured by their Module Size (sometimes called the X dimension). The Clearlmage Demo Application measures the Module Size as shown in the figure. The size should be at least 4 pixels, or 20 mil (.020 inches) for ID and for PDF417 barcodes. It should be more than 5 pixels, or 25 mil for DataMatrix.

Where should the barcode be placed?

Users often ask if the barcode should be placed in a particular place, or in a certain orientation. Good recognition software will find the barcode no matter where it is placed, and no matter the orientation. More importantly, barcode placement should follow two guidelines. Barcodes should be placed in areas where they are least likely to be damaged, by tears (near corners), by overwriting or stamps. On crowded forms, such as pathology lab authorizations, the barcode should not be located under a field where a user may write or sign their name, because the users will often extend their signature over the barcode.

Keep any form border lines or text from touching the barcodes, because they need a clear area surrounding the symbol. This is called the Quiet Zone or the Clear Zone. The size of the area can generally be no more than 20 or 25 mil. Using 1/16th of an inch is a good practice. If the form is printed in one step, and the barcode is printed subsequently in a second step, the printing tolerances may eat up the Quiet Zone; it would be wise to expand it to 1/8th or more. Good recognition software should tolerate violation of the Quiet Zone - however, as other defects accumulate on the image, performance will will invariably degrade.

Can Barcodes be Faxed?

Fax is our favorite business tool for workflow, because they are simple, easy to use, widespread, automatic and cheap; and they can facilitate any business process. As we all know, fax scanners exhibit a few weaknesses that have kept most users from taking full advantage of them as business process tools. Good barcode engineering practices can overcome these deficiencies, allow users to reap the benefits of fax machines and achieve high reliability in their business process. Let's analyze them one by one.

* In STANDARD resolution they car mangle barcodes

* Their scan quality is not great

* They sometimes swallow pages in the scan process

Fax machines support multiple scan resolutions for historical reasons. The so called STANDARD resolution, harks back to the days when a minute of telephone circuit time cost a considerable sum. Fax vendors developed a scheme which transmitted only half of the scan lines of the image, thereby reducing the cost of the fax by half. Thus STANDARD resolution scans at 98dpi in the vertical dimension and 204dpi in the horizontal. Barcodes are susceptible to significant impairment due to this effect.

The scan quality is to be endured, yet the usual business requirement is not to scan and view the fax image. Most often it is to know that the document was sent back to the originator with a signature or some comments, for compliance reasons. Correctly designed barcodes and good recognition software, capable of handling fax quality, can trigger a database update or a workflow action based on the receipt of a fax. Furthermore, good image repair software can properly reconstruct the image and correct many of the quality problems that the incoming fax images exhibit.

More importantly a well designed barcode system can track not only the entire document, but also the individual pages. The user can then rest assured that all the pages of an important document came through, and if not, which pages are missing, dramatically reducing the follow up workload.

How much damage can barcodes sustain?

Barcodes may be damaged by writing, stamping, coffee spills, poor printing (such as dot matrix printers on multipart forms), paper tears, creases, misfeeds in the scanner, streaks (caused by malfunctioning imaging elements in the scanners), scrapes, smudges, toner flaking, bleed-through, background interaction and many other reasons. 2D barcodes survive much better than 1D barcodes. The desired behavior from barcodes is to succeed, or to fail definitely. Delivery of incorrect data, known as a misread or a partial read is very bad because it can significantly impact the applications that rely on the data.

Older 1D symbologies such as Patch Codes, Code39, Codabar (used mainly by blood banks) and Code 2of5 (used on luggage tags by airlines) can survive hardly any damage. For that reason they are printed large and tall. The extra height affords them redundancy in case some portion of the barcode is damaged. What is worse, damage that occurs may be masked, leading to partial or misreads which delivers incorrect data to the application. These codes are also less robust because they are susceptible to misreads or read failures due to changes in the width of the bars and spaces, that can happen in faxing or low resolution scanning or reprinting.

Newer 1D symbologies such as Codel28 and Code93 automatically include a checksum system that identifies errors in the barcode data. Since they are edge to edge codes, they are less susceptible to scanning artifacts. They tend to survive more damage than their predecessors, and to either succeed or fail with no misreads.

The 2D symbologies contain significant error correction capability, in the same way as communication channels. Damage to the barcode generates errors in the raw data, which can be corrected so that the final data is clean and correct. The proportion of correctable errors as a percentage of the total data ranges from 0% to over 40%. When the number of induced errors exceeds the number that can be corrected a read failure how close the image is to the edge of the cliff.

Michael Salzman is the VP of Marketing at Inlite Research. He can be reached at sales@inliteresearch.com or 408-737-7092. Visit www.inliteresearch.com for additional information on barcodes.

Note: This is part of an on-going series of articles designed to prepare readers for the Information Capture Professional certification test. Information is extracted from several sources including TAWPI's ICP Handbook and will cover topics from each of the sections. The next testing window August 15, 2007 at TAWPI 2007 in Boston August 15-22, 2007 at LaserGrade Testing Centers December 1-8, 2007 at LaserGrade Testing Centers. For additional information visit www.tawpi.org/icp.htm/ or call Melissa Comeau at 617-426-1167 x12.

Copyright Association for Work Process Improvement May/Jun 2007
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