Anchor class for anchor-based object detectors.

min_level integer number of minimum level of the output feature pyramid.
max_level integer number of maximum level of the output feature pyramid.
num_scales integer number representing intermediate scales added on each level. For instances, num_scales=2 adds one additional intermediate anchor scales [2^0, 2^0.5] on each level.
aspect_ratios list of float numbers representing the aspect ratio anchors added on each level. The number indicates the ratio of width to height. For instances, aspect_ratios=[1.0, 2.0, 0.5] adds three anchors on each scale level.
anchor_size float number representing the scale of size of the base anchor to the feature stride 2^level.
image_size a list of integer numbers or Tensors representing [height, width] of the input image size.The image_size should be divided by the largest feature stride 2^max_level.





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Unpacks an array of labels into multi-scales labels.