Verification standards for 1D codes

ISO 15416, the standard for 1D codes, states that 10 separate scanlines must be created at the level of the code and each of these scanlines must be assigned to a class. Scanline categories are determined by examining seven different parameters; the parameter with the lowest rank becomes the total score for a single scanline. The final class is formed by the average of all individual line classes.

The first three parameters - minimum reflectivity, decoding and minimum edge contrast - were rated as pass or fail. If a scanline does not fulfil the minimum requirements for reflectivity, decoding or minimum edge contrast, it is automatically classified as ‘F’. If none of these three give cause for complaint, the software evaluates the parameters symbol contrast, modulation, defects and decodability. These are all assigned to one of the classes A to F. Once all scan lines have been classified, the ten scans are averaged to generate the final classification of the barcode.

Quality parameters

The minimum reflectance tests that the bars are dark enough to achieve the required ratio to the light reflected from the spaces
Edge contrast measures the difference between neighbouring bars and spaces
Modulation refers to localised deviations in contrast
Decoding checks whether the code can be read using the standard reference decoding algorithm
Defects include markings, printing errors or soiling that are located exclusively on a single bar or space
Decodability assesses the accuracy of the bar and space width compared to their ideal size. Barcodes with increased
or distorted bar widths are categorised in a low decodability class

Verification standards for 2D codes

For 2D codes, barcode verifiers check the reflection of the individual modules and the structure of the symbol. 2D codes are also evaluated according to the ISO 15415 standard using eight different parameters. Here too, some parameters are data-related and others are image-related. 2D codes contain much more data than 1D codes, which is why there are more parameters relating to both data quality and image quality.

The lowest individual parameter class counts as the overall class of the code. The evaluation process begins with a pass/fail test.If the code can be decoded, the first test is passed. If the code does not pass, the code is automatically categorised as class ‘F’. Afterwards, the reflection distance, symbol contrast, axial irregularities, modulation, grid irregularities, damage to the fixed pattern and error correction coefficient are tested.

Quality parameters

The symbol contrast indicates the difference between the darkest and the brightest modules
The local deviations of the contrast are measured by the modulation
Damage to the fixed pattern includes errors in the quiet zone, the L-sides and the clock pattern
The uneven scaling of the code shows the axial non-uniformity
Grid non-uniformity indicates the highest deviation from the grid