Understanding Barcode Verification Silence
Tuesday, November 18, 2008
Posted in: Tutorials
Understanding Verifier-Speak - and Silence
Understanding a verifier report can be a challenge—and I don’t mean relating “decodability” to your print process. There is plenty of information out there about that—and if you want our input about understanding any of the ANSI or Traditional parameters, just ask.
In fact, most—nearly all—of the questions we get are spoken in terms of a particular parameter or grade but pretty much nobody even notices it when the verifier fails, time after time, to produce a grade at all.
Scan—no result.
Scan—no result.
Scan—Symbol Grade D due to decodability.
Scan—no result.
Ditto four more times.
Client calls and asks about “decodability” without so much as a mention that it took 8 tries to get anything, but the anything (all one of it) was decodability.
Dare I say, “No it wasn’t” but then, I don’t even know about the eight deafening silences.
People, it means something when the verifier tries and fails to get even a decode. What does it mean? I have no idea—but it definitely means something. And it probably isn’t good—but it’s much, much worse if you don’t know what it is. And it will probably bite you.
A verifier is a very aggressive decoder. It has to be because it can’t grade a symbol if it can’t decode it.
Here’s another scenario we get a lot. The client is on the phone. His customer has complained, or even fined the client. So the client is trying to figure out what’s wrong, and maybe trying to build a defense. “The verifier is scanning the symbol with no problem” the client exclaims. “What’s the ANSI grade” we ask. “It’s an F but the symbol is scanning just fine!” the client spins.
So when the verifier with its very aggressive decode isn’t consistently decoding the symbol, it is significant. Very significant. And it leaves the user with pretty much no clue as to what’s wrong.
What to do.
The first thing to do is to get a low power magnifier—I prefer something around 8X but you may prefer something different. What you want to do is examine the narrow elements (bars and spaces). These are the building blocks of virtually every linear symbol. Most (but not all) linear symbols have only two element values: wide and narrow. UPC and Code 128 have more than two, but don’t let that discourage you. Look at the narrow bars—you should see that there are many of them across the symbol. Try to visually memorize how wide the narrow bar is—and then look at the narrow spaces. If they are not very similar in width to the narrow bar, this could be the source of your decode problem.
Next, using your magnifier, notice if there are defects in the symbol: voids in the bars and/or spots in the spaces: these can really confuse a verifier. A major void in a bar can look like two narrow bars with a narrow space between them; a spot in a space can look like an extra bar. Defects throw off the correct bar and space count in a symbol and a verifier doesn’t like this.
Now, examine the edges of the bars. Are they uneven or ragged? Are they different on the left side than on the right side? Are the bars wavy or jagged from the top of the symbol to the bottom?
Finally, notice if the bars are nice and opaque and the spaces nice and clean: there should be no show-through of the background through the bars. Ideally the bars should be black against a white background but if the barcode is printed in a color, the bars should never be a red or red-containing color. Green is usually OK for bars. Likewise the background is ideally white but should never be green or green-containing. Red is usually OK for the background.
Correct these problems if you can and rescan the symbol. Your decode rate should improve enough to show you what ANSI parameter is (or parameters are) controlling the final grade.
If all of these attempts fail, send an actual sample of the symbol or email a PDF of it to a reputable test lab for evaluation.
Another thing to pay attention to is when your verifier speaks in extremes—first an ANSI B, then an F, then an A, then a D. This is also significant but sometimes difficult to pin down.
Is the variability related to different areas in the barcode height? Does it tend to grade one way at the top and another way in the middle?
The key to solving many barcode quality issues is not to reply too heavily on the technology. Use your eyes. And if necessary, seek reputable help.
Is there a USPS Certification process for the new Intelligent Mail Barcode? We are a printer manufacturer and want to certify our printers as being IMB compliant.
Thanks,
Posted by on 01/21 at 10:31 AMRich