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# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
"""
Utility functions minipulating the prediction layers
"""
from ..utils import cat
import torch
def permute_and_flatten(layer, N, A, C, H, W):
layer = layer.view(N, -1, C, H, W)
layer = layer.permute(0, 3, 4, 1, 2) #N H W A C
layer = layer.reshape(N, -1, C) # N H*W*A C
return layer
def concat_box_prediction_layers(box_cls, box_regression):
box_cls_flattened = []
box_regression_flattened = []
# for each feature level, permute the outputs to make them be in the
# same format as the labels. Note that the labels are computed for
# all feature levels concatenated, so we keep the same representation
# for the objectness and the box_regression
for box_cls_per_level, box_regression_per_level in zip(
box_cls, box_regression
):
N, AxC, H, W = box_cls_per_level.shape
Ax4 = box_regression_per_level.shape[1]
A = 5
C = AxC // A # 1
box_cls_per_level = permute_and_flatten( box_cls_per_level, N, A, C, H, W)
box_cls_flattened.append(box_cls_per_level)
box_regression_flattened.append(box_regression_per_level)
# concatenate on the first dimension (representing the feature levels), to
# take into account the way the labels were generated (with all feature maps
# being concatenated as well)
box_cls = cat(box_cls_flattened, dim=1).reshape(-1, C)
box_regression = cat(box_regression_flattened, dim=1).reshape(-1, 4)
return box_cls, box_regression
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