Barcode Label Quality

Without verification, you do not know if you are printing barcode symbols that are readable when they are needed, particularly in a shipping environment where abrasion may reduce symbol readability.

In a traditional label analysis, a label is tested for compliance with a basic symbology specification. Typically the specification will call out requirements such as the character set, the widths of bars and spaces representing characters, the plus/minus tolerance for these widths, and the minimum acceptable print contrast. If the label fails to meet any of the requirements of the specification, it is deemed to be "out of spec."

However, the simple pronouncement that a label is "out of spec" says nothing about the severity of the problem. It may not even mean that the label cannot be read. Depending on the nature of the defects, the label might actually read well, not read - or worst of all - misread (i.e., the scanner sees a value that was not intended).

Finding this "all or nothing" approach to label analysis both unrealistic and uninformed, The American National Standards Institute (ANSI) decided to take a new approach to analyzing labels and determining their quality.

In the system recommended by ANSI, eight aspects of label quality are examined. An individual grade is given in each area (A,B,C,D, or F), and the "worst" of these grades becomes the overall profile grade. Four of the quality aspects are graded pass/fail, and four are graded A-F.

The four areas graded pass/fail are:

• DECODE - The label has all the required elements (check digit, guard bars, quiet zone, etc.) for the specified symbology, and decodes correctly.
• MINIMUM REFLECTANCE (Reflmin) - The percentage of reflectance for the most reflective space in the label must be at least two times the value for the least reflective bar in the label.
• MINIMUM EDGE CONTRAST (Ecmin) - The lowest reflectance difference found between any adjacent bar and space (or bar and quiet zone) must be at least 15%.
• ELEMENT DETERMINATION - There must be a single determinable edge between any two adjacent elements.

The four areas graded A through F are:

• SYMBOL CONTRAST (SC) - The percentage of difference between the least reflective bar and the most reflective space in the label. The higher this percentage is the better the grade.
• MODULATION (MOD) - Modulation is Ecmin divided by SC. The higher is this percentage is the better the grade.
• DEFECTS - A defect is defined as any time a single bar or space has more than one peak (or valley). The largest change in contrast within a bar or space is compared to the Symbol Contrast to determine the grade.
• DECODABILITY - ANSI has selected a benchmark decode algorithm for each symbology type. These algorithms allow for specific printing tolerances within which labels can still be correctly decoded. Decodability is the percentage of this tolerance remaining for the scanner to use (not used by printing error). The higher this percentage, the better the grade.

As stated above, the worst grade in any area becomes the overall profile grade. For example, if the label receives an "A" in seven areas but an "F" for Decodability, then the profile grade for that label is "F". The ANSI standard requires scanning the label a minimum of ten times, thereby producing ten overall profile grades. These ten profile grades are averaged together to produce the calculated symbol grade.