Comparison of multimodal RGB-thermal fusion techniques for exterior wall multi-defect detection

Exterior wall inspections are critical to ensuring public safety around aging buildings in urban cities. Conventional manual approaches are dangerous, time-consuming and labor-intensive. AI-enabled drone platforms have recently become popular and provide an alternative to serving automated and intelligent inspections. However, current identification only investigates RGB image of visual defects or thermal images of thermal anomalies without considering the continuous monitoring and the conversion between multiple defects. To gain new insights with modality-specific information, this research therefore compares the performance of early, intermediate, and late multimodal RGB-Thermal images fusion techniques for multi-defect detection in facades, especially for detached tiles and missing tiles. Numerous RGB and thermals images from an ageing campus building were collected as a dataset and the classical UNet for image segmentation was modified as a benchmark. The comparative results regarding accuracy (mAP, ROC, and AUC) proved that early fusion model performed well in distinguishing detached tiles and missing tiles from complex and congested facades. Nevertheless, intermediate and late fusion models were proven to be more efficient and effective with an optimal architecture, achieving high mean average accuracy with much less parameters. In addition, the results also showed that multi-modal fusion techniques can significantly improve the performance of multi-defects detection without adding a large number of parameters to single-modal AI models.