anchor box

A predefined reference box shape and size, tiled across the image, that a one-stage detector predicts offsets from.

An anchor box is one of a predefined set of reference box shapes and sizes, tiled densely across an image (or feature map) in advance, that a one-stage detector predicts a small offset and a class score from, rather than predicting a box's absolute coordinates from scratch at every location.

Examples

A one-stage detector tiles nine anchor boxes of different aspect ratios at every feature-map location, predicting only a small offset and a class score from whichever anchor fits an object best.