Background Thermal Compensation by Filtering for Contrast Enhancement in Active Thermography

A new contrast enhancement technique, called Background Thermal Compensation by Filtering (BTCF), is presented for application in active thermography inspection, based on median filtering with a decimated kernel to decouple the background thermal information from defective areas, without depending on any heat propagation model or the pre-selection of a healthy region. Furthermore, the selection of a reference thermogram is not needed unless a normalized version of the method is carried out. After decoupling the background thermal distribution, the enhanced contrast is obtained by applying the unsharp filtering strategy to only reveal the heterogeneities inside the material under analysis. Results obtained from CFRP slab inspection showthat BTCF can reduce the residuary non-uniformity heating by 70% and improves SNR values up to 15 dB when negative intensity values are truncated.