YOLO annotations are stored in .txt files. There are two different sub-formats available:
- bounding box format
- polygon format
The bounding box format has one line per annotation, using the following format:
class x_center y_center width height
The coordinates and dimensions are normalized (0-1) rather than absolute.
In order to accommodate mask/shape detection, a variant for managing polygons was introduced later, using this format:
class x0 y0 x1 y1 x2 y2 ...
The x/y coordinates are normalized as well (0-1).