Hardware free industrial anomaly detection using physics informed thermal proxies from RGB

Thermal infrared imaging is physically well-suited to industrial anomaly detection. However, calibrated thermal cameras cost thousands of dollars per device, making it inaccessible for most industrial environments. In this paper, this barrier is directly addressed. Under the assumption of thermal equilibrium and Lambertian surface conditions, Kirchhoff's law of thermal radiation implies that thermal emissivity and optical reflectance are complementary quantities. Since luminance approximates reflectance for Lambertian surfaces, the synthetic thermal proxy ε = 1 - L follows directly from standard RGB input. This proxy is validated against real lock-in thermography images, achieving polarity-corrected mean Pearson r = 0.4805, with r > 0.78 for Lambertian-compliant surfaces. This paper introduces ThermalCLIP, which combines this proxy with frozen CLIP ViT-B/16 patch features and PDE-based multiscale residuals. On highly repetitive textures, the physics-informed Laplacian residual provides discriminative signal that may complement appearance-based methods. Across all 15 MVTec AD categories, ThermalCLIP achieves a mean image level AUROC of 0.9441, and 0.8724 in zero-shot transfer to the VisA dataset.