DESTR: Object Detection with Split Transformer

Self- and cross-attention in Transformers provide for high model capacity, making them viable models for object detection. However, Transformers still lag in performance behind CNN-based detectors. This is, we believe, because: (a) Cross-attention is used for both classification and bounding-box regression tasks; (b) Transformer's decoder poorly initializes content queries; and (c) Self-attention poorly accounts for certain prior knowledge which could help improve inductive bias. These limitations are addressed with the corresponding three contributions. First, we propose a new Detection Split Transformer (DESTR) that separates estimation of cross-attention into two independent branches — one tailored for classification and the other for box regression. Second, we use a mini-detector to initialize the content queries in the decoder with classification and regression embeddings of the respective heads in the mini-detector. Third, we augment self-attention in the decoder to additionally account for pairs of adjacent object queries. Our experiments on the MS-COCO dataset show that DESTR outperforms DETR and its successors.