How the ISOIEC standard for 2D barcode print quality is changing

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How the ISO/IEC standard for 2D barcode print quality is changing

ISO/IEC 15415, the standard for measuring the quality of printed 2D barcodes was first introduced in 2004. It was revised in 2011, and now a new version has been published.

The main changes will be as follows:

the introduction of continuous (or decimal) grading;
the introduction of a more optimal threshold calculation;
introduction of a more stable symbol contrast calculation;
a grading for print growth;
the combination of modulation and reflectance margin into a single measurement.

The major change is that the grading of parameters will now be stated to one decimal place rather than with integer values, meaning that the grading is more granular, and more precise. Some 2D codes that previously failed will now receive a passing grade with the 2024 version of ISO/IEC 15415.

There is also the introduction of a new graded parameter, print growth. This reflects the increase or decrease in the size of the modules from their ideal size, and it will be assessed for both the width and height of the modules. The worse print growth in either direction will form the basis of this grading.

The determination of the threshold (no longer named ‘global threshold’) – the value which determines whether a module is regarded as light or dark - has been optimised, and is no longer the halfway point between the lightest and darkest pixels.

Symbol contrast is now no longer calculated using the values of the lightest and darkest pixels, but uses the values of 1% of the lightest and 1% of the darkest pixels to produce a more consistent measure. This means that symbol contrast will be reduced slightly, which has the consequence of affecting the modulation grade.

Modulation and reflectance margin parameters are now measured as one parameter, modulation.

Changing from integer to decimal grading

The table below shows how percentage values for some of these parameters became integer grades before this new 2024 release:

This approach has meant that a symbol that has a symbol contrast value of 67% [with all other parameters being grade 4.0) would have an overall grade of 3.0.

The 2024 version of ISO/IEC 15415 recognises that a symbol like this should have a better grade than an otherwise similar symbol where the symbol contrast value was, say, 57%. So now the conversion of percentages to grade values is done with 41 bands rather than only five, and this means that barcodes will generally have slightly better grades than they did before. It means that small changes in parameter values at the transition points between grades will not cause such a large change in the grade.

Grade	Symbol contrast	Modulation and Reflectance Margin	Axial Non-Uniformity	Grid Non-Uniformity	Unused Error Correction
4	≥ 70%	≥ 50%	≤ 6%	≤ 38%	≥ 62%
3	≥ 55%	≥ 40%	≤ 8%	≤ 50%	≥ 50%
2	≥ 40%	≥ 30%	≤ 10%	≤ 63%	≥ 37%
1	≥ 20%	≥ 20%	≤ 12%	≤ 75%	≥ 25%
0	< 20%	< 20%	> 12%	> 75%	< 25%

Here are two tables that show how the parameter percentages have become fractional grades for the five parameters referred to above and for the new parameter, print growth.

Two other parameters, decode, and fixed pattern damage are also assessed. Decode is either pass or fail (4.0 or 0.0), while fixed pattern damage is assessed and graded continuously. Fixed pattern damage is the parameter that grades damage to the finder pattern, quiet zone, and other fixed patterns in a symbol; the patterns to be considered are specified independently for each symbol.

The overall grade for a symbol is the lowest value of any of these parameters. The reporting of the final grade of a barcode is unchanged, so it will still appear in the form n.n/aa/www, where ‘n.n’ is the numeric grade, ‘aa’ the aperture reference, and ‘www’ the wavelength of light used, measured in nanometres.

The graphs below show how the percentage values for each of these graded parameters are converted into decimal grades. It is easy to see that any percentage value will never receive a lower grade than it did before, and that most grades will be higher.

ISO/IEC Grade	ANSI Grade
3.5 - 4.0	A
2.5 - 3.4	B
1.5 - 2.4	C
0.5 - 1.4	D
0 - 0.4	F

Grade	Symbol contrast	Module grading for modulation	Unused error correction
4.0	≥ 70%	≥ 50%	≥ 62.0%
3.0 to 3.9	55.0% to 69.9%	40.0% to 49.9%	50% to 61.9%
2.0 to 2.9	40.0% to 54.9%	30.0% to 39.9%	37% to 49.9%
1.0 to 1.9	20.0% to 39.9%	20.0% to 29.9%	25% to 36.9%
0.1 to 0.9	15.5% to 19.9%	17.75% to 19.9%	20.5% to 24.9%
0.0	≤15%	≤ 17.5%	≤ 20%

Grade	Axial non-uniformity	Grid non-uniformity	Print growth
4.0	≤ 6.0%	≤ 38.0%	≤ 10.0%
3.9 to 3.0	6.1% to 8.0%	38.1% to 50.0%	10.1% to 28.0%
2.9 to 2.0	8.1% to 10.0%	50.1% to 63.0%	28.1% to 34.0%
1.9 to 1.0	10.1% to 12.0%	63.1% to 75.0%	34.1% to 40.0%
0.9 to 0.1	12.1% to 13.8%	N/A	40.1% to 60.0%
0.0	≥ 14%	> 75.0%	> 60%