YOLO-AlignRank: Cross-Scale Deformable Head and Rank-Consistent Loss for One-Stage Object Detection
Run Li, Fangjun Liu · Frontiers in Computing and Intelligent Systems · 2025
Single-stage object detectors dominate industrial deployment thanks to end-to-end simplicity and low latency, yet a persistent bottleneck is the misalignment between classification confidence and localization quality. Because candidate ordering before and after NMS is largely driven by classification scores, high-IoU predictions are often suppressed while poorly localized but high-score boxes survive. Prior quality-aware classification methods partly mitigate this issue, but stop short of a systematic solution that spans cross-scale representation and ranking consistency. Meanwhile, the YOLO family has advanced with decoupled heads, dynamic label assignment, and even NMS-free training, creating an opportunity to unify head structure, quality learning, and ranking constraints. We propose YOLO-AlignRank, which integrates two complementary innovations. First, the CSD-Head (Cross-Scale Sparse Deformable Head) augments a YOLO decoupled head with cross-scale sparse deformable sampling and a Bidirectional Cross-Scale Dynamic Fusion (BCDM) module. A small set of learnable offsets samples key points from adjacent pyramid levels, inheriting the spatial adaptivity of DCNv2 and the sparse-attention spirit of Deformable DETR while preserving convolutional efficiency. BCDM then performs gated top-down and bottom-up feature fusion via lightweight dynamic convolution, achieving real-time multi-scale integration akin to PAN/BiFPN. Second, the RCQ-Loss (Rank-Consistent Quality Loss) extends quality-aware classification with intra-set list alignment and pairwise ranking regularization. For each ground-truth object g with candidate set Sg, RCQ-Loss aligns the distribution of classification scores with normalized localization qualities (proportional to IoU) within Sg and enforces matching order. Concretely, a soft distribution-alignment term (softmax cross-entropy over Sg) and a pairwise hinge term ensure that high-IoU candidates receive higher scores than low-IoU ones, enforcing consistency in both score distribution and sorted order. Together, these components align confidence with IoU across scales and candidate sets, reduce pre- and post-NMS mis-ranking, and improve multi-scale detection accuracy while retaining YOLO-level real-time efficiency and end-to-end simplicity in practical deployments.