What makes code readable or illegible

Reasons for illegible barcodes

Barcodes are generally considered to be a very reliable method of collecting data. However, a few typical errors can occur with this technique as well.


Subsequent refinements, such as the application of a film lamination or packaging made of shrink film, can make the barcode illegible for the scanner. Read errors can occur, particularly if the barcode's quiet zone (free area around the code) is disturbed by post-processing.

The recommendation is therefore to always test barcodes in their final form or on the final product.

Pressure increase

In many printing processes there is what is known as "pressure increase". This means that the printed lines are wider in practice than in the original. In some printing processes (offset printing) this is due to the pressure used, which pushes the print dots wider. In other cases it is due to the ink bleeding (inkjet).

Barcodes per se have a certain tolerance against changes in the width of the bars. However, if the pressure increase is too great, the code becomes more difficult to scan.

Use suitable printers such as thermal transfer printers with sharp edges and a suitable print resolution for your application.

Color combinations

There are certain color combinations that are particularly difficult to read. These include red barcodes on a white background and black codes on a green background.

Always choose colors with a high contrast between the strokes and the background and avoid the problematic combinations.

see also: main article barcode colors for an overview of the favorable and unfavorable color combinations

Transparent substrates

Barcodes printed on transparent or translucent packaging such as plastic bags are difficult to read if dark content shows through the packaging and the contrast between the barcode and the background deteriorates.

Avoid translucent barcodes.

Material properties

Especially on metal, such as aluminum cans, but also on glossy paper, there are often high error rates when reading barcodes. The barcode is clearly visible to the human eye and the material is highly reflective. However, the properties of the light used by the scanner can differ, so that it is either not reflected or is strongly scattered. The scanner then no longer recognizes the contrast between lines and gaps.

The problem can often be avoided if the barcode is printed inverted: Instead of printing black lines on metal, white gaps are printed so that the unprinted metal forms the lines.

Quiet areas

There must be defined quiet zones around every barcode so that the scanner recognizes where the code begins and ends. The quiet zones must not be printed in order not to impair legibility.

Make sure that there are sufficient quiet areas around the barcode during the design and layout.

see also main article: quiet zone

Corners and edges

Placing barcodes on corners and edges can lead to a practical violation of the quiet zone. By eliminating the material, the scanner cannot see a light background.

Quiet zones must always be fully visible on the print material, barcodes must not be placed directly at the edge.

Corrupt data

Problems with the coding of the data can arise, especially with more complex codes, such as GS1. In some cases, the data must be encoded in the correct format so that even specifying the date in the wrong order (day / month / year) can lead to an incorrect barcode.

Inverted barcodes

In and of themselves, barcodes must not be inverted. The black lines must remain black (for the scanner). However, if the printing ink is white on black packaging, an inverted barcode can be printed so that the white spaces are printed and the black lines are created through the background. In this case, the quiet zone must also be printed in extra white.

See also

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