how to modify anchor box?

[cjt222]

hello，i want to modify ratio of anchor(i need 7 ratio),but when i modify anchor in util/anchor.py,it cause some problem,what parameters should i modily?

[hgaiser]

Currently there is no easy method to configure this (see #324). Anchors are generated in two places unfortunately, once for creating the target data (which is the one you edited) and once for inference, which is the one you didn't edit: https://github.com/fizyr/keras-retinanet/blob/master/keras_retinanet/layers/_misc.py#L31-L45

[cjt222]

thank you for your answer， i have also changed number of anchors in keras_retinanet/vim keras_retinanet/models/retinanet.py，it is ok!!!

[hgaiser]

Ah that would work for training, but it would still break when doing inference. It reminded me that my previous comment was wrong though, for inference it is better to create an AnchorParameters object like this :

anchor_parameters = keras_retinanet.models.retinanet.AnchorParameters(
    sizes   = [32, 64, 128, 256, 512],
    strides = [8, 16, 32, 64, 128],
    ratios  = np.array([0.5, 1, 2], keras.backend.floatx()),  # Change this for your ratios
    scales  = np.array([2 ** 0, 2 ** (1.0 / 3.0), 2 ** (2.0 / 3.0)], keras.backend.floatx()),  # Change this for your scales
)

Which you then should be able to pass to this line like so:

 model = model_with_weights(backbone_retinanet(num_classes, backbone=backbone, modifier=modifier, anchor_parameters=anchor_parameters), weights=weights, skip_mismatch=True)

I haven't tried this yet though, so I don't know if it works or not..

[cjt222]

ok， i see, thank you so much!!!!