2.1.3. Feature Pyramid Recovery

As shown in Figure 6, the fused feature maps are restored to a feature pyramid through up-sampling and max-pooling. This part can be regarded as the reverse operation of feature fusion. As shown in Figure 6, the enhanced feature maps *H* from the non-local module are restored to a feature pyramid consisting of five levels {*F***1**, *F***2**, *F***3**, *F***4**, *F***5**}. Among them, {*F***1**, *F***2**} are obtained from *H* through max-pooling. {*F***4**, *F***5**} are obtained from *H* through up-sampling. Feature maps *H* are retained as *F***3** in the recovered feature pyramid. In the recovered feature pyramid, each level contains more multi-scale features and balanced information from all resolutions. To conclude, the BAFPN enables RBFA-Net to better focus on multi-scale ship features while integrating global features.

**Figure 6.** Architecture of feature pyramid recovery.
