FPG

Feature Pyramid Grids, or FPG, is a deep multi-pathway feature pyramid, that represents the feature scale-space as a regular grid of parallel bottom-up pathways which are fused by multi-directional lateral connections. It connects the backbone features, $C$, of a ConvNet with a regular structure of $p$ parallel top-down pyramid pathways which are fused by multi-directional lateral connections, AcrossSame, AcrossUp, AcrossDown, and AcrossSkip. AcrossSkip are direct connections while all other types use convolutional and ReLU layers.

On a high-level, FPG is a deep generalization of FPN from one to $p$ pathways under a dense lateral connectivity structure.