WSO-YOLO11: a wavelet–strip-oriented YOLO11 framework for hot-rolled steel strip surface defect detection

Surface defects on hot-rolled steel strips are often small, slender, strip-like and low-contrast, so high-frequency details and elongated structures can be lost during conventional convolutional downsampling and feature fusion. To address these issues, we propose Wavelet-Strip-Oriented YOLO11 (WSO-YOLO11), a wavelet-strip prior enhanced network based on YOLO11s. A Wavelet-Space-to-Depth Hybrid Stem (WSH-Stem) is introduced into the shallow backbone to preserve fine-grained textures, and an Orientation-Strip Residual Neck (OSR-Neck) is integrated into the FPN/PAN structure to strengthen the continuous perception of narrow defects. WSO-YOLO11 contains about 9.0M parameters, approximately 4.3% fewer than YOLO11s. On NEU-DET, WSO-YOLO11 improves mAP@0.5 from 73.5% to 75.8%, mAP@0.5:0.95 from 38.2% to 39.7%, and F1 from 68.1% to 69.3%. On GC10-DET, X-SDD and KSDD2, it also improves mAP@0.5, with the largest gain reaching 3.4 percentage points. These results indicate that WSO-YOLO11 achieves moderate improvements in mAP-related metrics while maintaining a compact model size, and shows relatively stable detection performance across multiple steel strip surface defect datasets.