UAV-based panoramic imaging for automated bughole segmentation and quantitative color-difference assessment of concrete bridge piers

As key load-bearing elements, bridge piers are highly sensitive to concrete construction quality, which directly affects structural safety and durability. Surface defects such as color differences and bugholes are common and, if not properly assessed, may accelerate deterioration. To overcome the limitations of conventional inspection methods in precision, efficiency, and objectivity, this study proposes an intelligent framework integrating high-resolution panoramic imaging, deep semantic segmentation, and spatial color-difference analysis. The main contributions include: (1) A segment-based matrix image acquisition strategy is developed using unmanned aerial vehicles, combined with a DSeam-driven deep stitching algorithm to generate panoramic images of piers with geometric consistency and luminance continuity, serving as a unified visual basis for defect recognition. (2) For bughole segmentation, a PoreMamba-Net semantic network based on a state space modeling architecture is constructed. The network employs multi-branch convolution and selective scanning mechanisms to enhance fine-grained perception and contextual representation of small targets, enabling high-precision segmentation. A quantitative evaluation system composed of the apparent bughole area ratio, maximum bughole diameter, and bughole distribution standard deviation is further proposed to comprehensively characterize bughole quantity, size, and spatial uniformity. (3) For unbounded and non-structural color difference defects, a pixel-level analysis method is proposed by combining multi-scale retinex with color restoration-based illumination normalization and the CIE94 color difference model. Moran’s I spatial autocorrelation index is introduced to jointly quantify color deviation intensity and spatial consistency, supporting classification of color differences and detection of clustered anomalies. The proposed framework is validated on typical piers from the Shiziyang Channel Bridge construction project in Guangdong Province. Results demonstrate strong adaptability, robustness, and accuracy in complex field conditions, providing reliable technical support for concrete quality acceptance and lifecycle management.