Overview
EN ISO 21227-2:2006 / ISO 21227-2:2006 defines an objective, image‑based procedure for evaluating multi‑impact stone‑chipping damage on coated surfaces. Using digital optical imaging and image analysis, the standard replaces or complements subjective visual assessments by calculating the percentage of damaged area and converting that value to the ISO 20567‑1 rating scale. The document was prepared by ISO/TC 35 and is endorsed by CEN (EN ISO 21227‑2:2006).
Key topics and technical requirements
- Principle: Acquire a digital image of the impact area, convert to grey‑scale or colour, apply thresholding to produce a binary image where damaged areas are dark and undamaged areas are light, then compute damaged area as a percentage of the region of interest (ROI).
- Region of interest (ROI): Preferred ROI is 70 mm × 70 mm; smaller ROIs may be used if they do not change results by more than half a rating (ISO 20567‑1).
- Image resolution: Minimum 6 pixels per millimetre to ensure reliable area measurement.
- Illumination: Diffuse bright‑field illumination is recommended so damaged areas are clearly distinguished; direct lighting may detect non‑stone‑chip artefacts.
- Calibration: Use a set of reference panels (prepared in the same laboratory and following ISO 20567‑1 ratings) to fix image acquisition parameters and verify repeatability of the imaging/evaluation system.
- Evaluation & rating: Determine damaged area percentage and express it as a rating on the 0 to 5.0 scale from ISO 20567‑1 (half‑point results allowed, e.g., 3.5).
- Extended analysis: Optionally determine contributions from individual coating layers (delamination/flaking across layers is included in damage).
- Precision: An international round‑robin established reproducibility limits for two damage levels (example reproducibility R values reported in the standard).
- Test report content: Must include coating identification, reference to ISO 21227‑2, illumination and imaging setup, resolution and image parameters, processing details, test result, deviations, anomalies, date and operator.
Applications and who uses it
- Coating manufacturers for objective stone‑chip resistance characterization and QC.
- Automotive and transport OEMs to evaluate protective topcoats and primers against multi‑impact damage.
- Laboratories and standards testing facilities implementing ISO 20567‑1 multi‑impact tests and seeking quantitative image analysis.
- R&D teams developing formulations or pretreatment processes where layer‑specific damage analysis is required.
Related standards
- ISO 20567‑1 - Describes the multi‑impact stone‑chip test method used to simulate damage.
- ISO 21227‑1 - General guidance on optical imaging evaluation of coated surfaces.
- ISO 21227‑3 - Evaluation of delamination and corrosion around a scribe (related part of the series).
Keywords: stone‑chipping, optical imaging, coated surfaces, paint and varnish evaluation, ISO 21227‑2, EN ISO 21227‑2, image analysis, stone chip resistance.
