// Key takeaways
- ISO/IEC 29158 adapts 2D grading to codes marked on metal, plastic and other part surfaces.
- It allows lighting set-ups other than the single 45-degree arrangement used for printed codes.
- GS1 writes a grade measured this way with a DPM prefix and the lighting set-ups it permits.
- Reading a part mark on the line is not grading it; a formal grade needs a verifier set up for DPM.
What does ISO/IEC 29158 cover?
ISO’s abstract for the 2025 edition says the document describes modifications to the symbol quality method of ISO/IEC 15415 and provides a symbology specification. It establishes alternative illumination conditions, some new terms and parameters, changes to how certain parameters are measured and graded, and how results are reported. ISO names its audience as verifier manufacturers and the people who write application specifications, not line operators.
The name has changed over time. ISO’s catalogue lists ISO/IEC TR 29158:2011 and ISO/IEC 29158:2020 as the Direct Part Mark (DPM) Quality Guideline; the second edition, published in March 2025, is titled a bar code symbol quality test specification for direct part marks. Many documents still use the older name: the 2026 GS1 General Specifications refer to ISO/IEC TR 29158, also called AIM DPM. According to GS1’s DataMatrix guideline, the work began when AIM, the industry association for automatic identification, acknowledged that ISO/IEC 15415 alone was not sufficient for marks made directly on parts.
Why do direct part marks need different lighting and grading?
A printed code is dark ink on a light, fairly matt label, and lighting at 45° shows it well. A direct part mark is different. Dot-peen dots are small craters whose contrast comes from shadows and edges. Laser marks change the colour or texture of the surface. Machined, cast or polished metal adds glare, tooling marks and curvature. Under label-style lighting, a mark that reads well under suitable light can look poor, and the grade would say more about the lighting than about the mark.
That is why ISO’s own note to ISO/IEC 15415 says that grades for direct part marks agree better with real reading performance when ISO/IEC 29158 is used alongside it. GS1’s marking advice points the same way: it warns against finishes that cause heavy shadowing or glare, and against surfaces offering less than 20% difference in reflectance between mark and part. According to GS1’s DataMatrix guideline, the DPM document adds parameters such as modulation within a cell, which checks that each cell is even in itself. How we light marks for reading is covered in our machine vision lighting guide and on the DPM code reading page.
How does ISO/IEC 29158 compare with ISO/IEC 15415?
ISO/IEC 29158 is not a separate scale. It keeps the 2D method and the 4-to-0 grades and changes the conditions and some measurements, so that the grade reflects the mark rather than the way it was lit.
| Aspect | ISO/IEC 15415 | ISO/IEC 29158 |
|---|---|---|
| Written for | Printed 2D symbols: labels, packs, documents | Codes marked directly on the surface of an item |
| Relationship | A complete test specification in its own right | Modifies the ISO/IEC 15415 method; the two are used together |
| Lighting | 45° by default; GS1 notes the standard also provides for 30° and 90° | Alternative illumination conditions suited to marked surfaces |
| Parameters | The standard 2D set: contrast, modulation, fixed pattern damage, grid, error correction | New terms and parameters and changed measurement of some existing ones |
| Typical marks | Thermal transfer, ink-jet and printed labels | Dot-peen, laser marking, chemical etching; ink-jet on parts in some applications |
| How GS1 writes the grade | For example 1.5/20/660 | Prefixed DPM, with an aperture range, 650 nm and the permitted lighting set-ups |
How does GS1 apply ISO/IEC 29158?
GS1’s symbol specification table for direct part marking shows how an application standard uses it. For GS1 DataMatrix and GS1 QR Code marked directly on items other than medical devices, the minimum is 1.5/06/660. Ink-based direct marking of medical devices is set at 1.5/08/660. For non-ink marks on small medical and surgical instruments, GS1 separates two types: marks with connected modules in the finder pattern, made by laser or chemical etching, and marks with separate dots, made by dot-peen. Each has its own X-dimension range and a grade written like DPM1.5/08-20/650/… followed by the lighting set-ups allowed.
GS1 explains that the DPM prefix means the grade was obtained under the DPM document rather than plain ISO/IEC 15415, and that it normally sets the aperture at 80% of the smallest X-dimension allowed. The lighting codes themselves are defined in the ISO text, which is not public, so we do not interpret them here.
What can a DPM reader on the line show?
A fixed code reader at a set point in the process shows whether each mark decodes, whether the serial or part number is the one expected, and writes the result to the PLC or MES. A trend of failed or marginal reads is an early sign that a stylus is wearing or laser settings have drifted. It does not give an ISO/IEC 29158 grade: that needs a verifier with DPM lighting, calibrated and run under the conditions the application specifies. addaScan integrates HIKROBOT ID code readers for reading; we do not supply verifiers or formal grading.
Frequently asked questions
Is ISO/IEC 29158 a guideline or a standard?
Do I need ISO/IEC 29158 for an ink-jet code on a part?
Who decides which DPM grade a part needs?
Sources
- ISO/IEC 29158:2025, bar code symbol quality test specification, direct part mark (catalogue abstract) (ISO, read 2026-10-03)
- ISO/IEC 15415:2024 (catalogue abstract, note on direct part marks) (ISO, read 2026-10-03)
- GS1 General Specifications, Release 26.0 (symbol specification table 7, direct part marking; §5.12.4.3) (GS1, read 2026-10-03)
- GS1 DataMatrix Guideline, Release 2.5.1 (§4.6.2, other print quality standards) (GS1, read 2026-10-03)