Why Your 2D Code Can't Be Read and Barcode Identification Criteria

2D codes can vary greatly in their readability. Although it's obvious that some codes will fail more than others, from codes written with supposedly perfect laser marking devices to symbols written with mechanical engraving and dot matrix systems. The problem with bad code is that it can really screw things up. Medical devices can be stripped of their entire history of use, or a perfect aircraft or automotive part can be thrown away due to an unreadable code.

Since readability is such an important issue, the International Organization for Standardization (ISO) has written some guidelines, known as ISO/IEC 15415, which specify what a readable code should look like. A well-formed, two-dimensional code is determined by eight different parameters. Let's take a look at each of these.

SYMBOL CONTRAST

Since barcodes consist of light and dark elements, there must be a difference between the two. Contrast, or the difference in intensity between the light and dark elements of a symbol, is an important component of readability.

MODULATION

There are high contrast barcodes and there are low contrast barcodes. There are also barcodes with high-contrast and low-contrast areas (usually due to inadequate ink dispersion). Consistency of contrast across a symbol is known as modulation. Many readers use algorithms to correct for low contrast, but when the contrast varies wildly from corner to corner this may be impossible for the reader to read or may need more time processing the code.

Three arrows point to places where the contrast of the datamatrix symbol with a low modulation degree decreases.

AXIAL FORM DISORDER

Most two-dimensional codes consist of individual squares, and to the average reader it is important that they are actually squares. If these cells look like rectangles - either because they are too long or too wide - then the symbol containing them will have a low rating in terms of their axial form.

This 2D code is significantly axially distorted.

GRID FORM DISORDER

Like axial irregularity, grid irregularity deals with the "squareness" of the component cells of a symbol. However, in this case, the measurement looks at the level of tension that lies within the symbol occurring diagonally along the x or y axes. Basically, if the squares start to look kite-shaped, then the grid irregularity of the symbol is a problem.

This 2D code shows significant grid irregularity.

FIXED PATTERN DAMAGE

Most barcode formats or symbologies contain certain mandatory patterns that are necessary to indicate to readers their presence as well as the number of rows and columns. For example, Datamatrix symbology always has a “finding pattern”—two adjacent borders of black cells (L Pattern)—and a Clock Pattern—two borders with alternating dark and light cells. Any degree of damage that prevents the detection of these patterns will be taken into account.

Three arrows show where a 2D code has Pattern damage.

CELL PRINTING ERRORS

Given the overall size of a code and the number of rows and columns, the expected cell size can be easily calculated. But sometimes, either the black cells or the white cells will be larger than expected. This usually happens due to printing problems. If the ink exceeds the cell boundaries, the black cells will be too large. Otherwise, if there is not enough ink, the white cells may be excessively large.

REFLECTION PARAMETER

The overreflection parameter generally looks at the black and white threshold of the cells. This is something like contrast, but instead of measuring the difference in intensity, it measures the likelihood that contrast problems - or problems with light reflecting off the surface of the code - will cause errors.

LEGIBILITY

The degree of readability is determined by how well a symbol can be resolved relative to an ideal two-dimensional symbol of exceptional quality.

As you can see, many parameters are involved in classifying two-dimensional codes. Of course, some things will never be perfect, such as the degree of reflection margin for a shrink-wrapped code.

As a result, many codes have various difficulties.

However, industrial code reader manufacturers are working at full speed to overcome these challenges.

Omron microscan has developed an algorithm that ensures readability even in these difficult conditions.

The guarantee of fast and accurate readings even in the worst conditions is a great benefit for manufacturers who want trouble-free traceability. Barcodes are often imperfect, but with X-Mode, imperfections will rarely stop the production line.