how to configure stretching vs. letteboxing

[LukeAI]

I understand that by default, darknet (in this repo.) will stretch images to the network dimensions during training. Is it possible to configure it to preserve aspect ratio with letterboxing instead?

[AlexeyAB]

By default this repository resizes images to the network size (width= and height= in cfg-file) without keepeing aspect ratio: #232 (comment)

To keep aspect ratio:

• during Training: set letter_box=1 in the [net] section in cfg-file

• during Detection and checking mAP: use flag -letter_box in the command
  ./darknet detector map cfg/coco.data cfg/yolov3-spp.cfg yolov3-spp.weights -letter_box

[lq0104]

hi @AlexeyAB , my question is does the cmd "darknet detector calc_anchors" supports "letteboxing" option? I think if I have trained dataset with the "letteboxing" option, is it better to use anchors with the same option?

[AlexeyAB]

@lq0104
No, it calc_anchors doesn't support letterboxing.

Yes, may be we should implement it.