How can you determine what bar code colors are acceptable for linear bar codes? Do you have to actually print a bar code before you can tell if it will work?
No! It's pretty easy to test possible colors for the bar code and/or the background to gauge the quality.
Bear in mind, however, you may or may not exactly duplicate the color swatches you are using for your test.
There are many factors involved in producing an exact bar code color match so be aware, this test will only get you in the ballpark.
A good rule of thumb is, if your test results indicate the colors you are testing produce just a marginally safe result, it’s probably wise to use a color or color combination with less marginal results.
The bottom line issue is color contrast, or in barcoding, the term used is Symbol Contrast.
How is Symbol Contrast measured and where is the threshold between acceptable and unacceptable results?
Symbol Contrast (SC) is a straight subtraction of the minimum reflectance value (Rmin) from the light reflectance value (Rmax). These values should be expressed as percentages.
The Rmin is always the color for the bars; the Rmax is always the background color. The threshold is 40% to achieve an ANSI/ISO C grade, but if you’re printing a barcode on corrugated, the threshold is 20% for an ANSI/ISO D.
Let’s say you want to print an ITF14 on corrugated using a combination of green and red for the barcode and background. If you use a reflectance densitometer, make sure it has a 660nm (+ 10nm) red light source. A white light reflectance densitometer will not work for this.
Some verifiers can be used as reflectance densitometers and can collect Rmin and Rmax values automatically—and some will even do the SC calculation for you.
Looking at the Details panel in the upper right quadrant of the Axicon Verifier report, our green and red bar code colors will produce a Symbol Contrast value of 70% – perfectly acceptable for printing a barcode.
Notice in the Scan Reflectance Profile panel at the bottom of the Axicon Verifier report, that the Static Reflectance option is enabled (checked). This sets the verifier to operate as a reflectance densitometer without testing an actual barcode.
Simple and quick! But remember—this is the result for these particular barcode colors.
For you to achieve these same results you must duplicate these exact colors as best you can. But having achieved an SC of 70%, you‘ve got a lot of latitude! This is a pretty safe color combination.
A 30-year veteran of the bar code industry, John Nachtrieb and his company Barcode-Test help provide solutions for customers' bar code quality challenges. He assists product managers, package printers, and suppliers by managing bar code related risk, and supporting bar code integrity over the long haul. You can find more of his writing on bar code quality at the Barcode-Test blog.
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