🤖 AI Summary
This study addresses the challenge of defect visibility fluctuation in time/frequency domains during infrared thermography post-processing, which hinders automated unsupervised analysis due to conventional evaluation metrics’ reliance on prior knowledge of defect locations or defect-free reference regions. To overcome this limitation, the work proposes a data-driven, spatial-prior-free approach that adapts the concept of representative elementary volume into two dimensions for infrared thermography and integrates three no-reference metrics: a homogeneity index (HI) based on local intensity distribution deviation, a representative elementary area (REA) derived from Minkowski functionals, and a geometric-topological total variation energy (TVE). Validated on pulsed thermography sequences of a carbon-fiber-reinforced polymer plate containing six artificial defects, the method enables robust and unbiased frame ranking, offering a reliable basis for automated defect detection through optimal image selection.
📝 Abstract
Infrared thermography (IRT) is a widely used non-destructive testing technique for detecting structural features such as subsurface defects. However, most IRT post-processing methods generate image sequences in which defect visibility varies strongly across time, frequency, or coefficient/index domains, making the identification of defect-representative images a critical challenge. Conventional evaluation metrics, such as the signal-to-noise ratio (SNR) or the Tanimoto criterion, often require prior knowledge of defect locations or defect-free reference regions, limiting their suitability for automated and unsupervised analysis. In this work, a data-driven methodology is proposed to identify images within IRT datasets that are most likely to contain and represent structural features, particularly anomalies and defects, without requiring prior spatial information. The approach is based on three complementary metrics: the Homogeneity Index of Mixture (HI), which quantifies statistical heterogeneity via deviations of local intensity distributions from a global reference distribution; a Representative Elementary Area (REA), derived from a Minkowski-functional adaptation of the Representative Elementary Volume concept to two-dimensional images; and a geometrical-topological Total Variation Energy (TVE) index, also based on two-dimensional Minkowski functionals, designed to improve sensitivity to localized anomalies. The framework is validated experimentally using pulse-heated IRT data from a carbon fiber-reinforced polymer (CFRP) plate containing six artificial defects at depths between 0.135 mm and 0.810 mm, and is further supported by one-dimensional N-layer thermal model simulations. The results demonstrate robust and unbiased ranking of image sequences and provide a reliable basis for automated defect-oriented image selection in IRT.