def bottleneck(inp, output, internal_scale=4, asymmetric=0, dilated=0, downsample=False, dropout_rate=0.1):
# main branch
internal = output // internal_scale
encoder = inp
# 1x1
input_stride = 2 if downsample else 1 # the 1st 1x1 projection is replaced with a 2x2 convolution when downsampling
encoder = Conv2D(internal, (input_stride, input_stride),
# padding='same',
strides=(input_stride, input_stride), use_bias=False)(encoder)
# Batch normalization + PReLU
encoder = BatchNormalization(momentum=0.1)(encoder) # enet uses momentum of 0.1, keras default is 0.99
encoder = PReLU(shared_axes=[1, 2])(encoder)
# conv
if not asymmetric and not dilated:
encoder = Conv2D(internal, (3, 3), padding='same')(encoder)
elif asymmetric:
encoder = Conv2D(internal, (1, asymmetric), padding='same', use_bias=False)(encoder)
encoder = Conv2D(internal, (asymmetric, 1), padding='same')(encoder)
elif dilated:
encoder = Conv2D(internal, (3, 3), dilation_rate=(dilated, dilated), padding='same')(encoder)
else:
raise(Exception('You shouldn\'t be here'))
encoder = BatchNormalization(momentum=0.1)(encoder) # enet uses momentum of 0.1, keras default is 0.99
encoder = PReLU(shared_axes=[1, 2])(encoder)
# 1x1
encoder = Conv2D(output, (1, 1), use_bias=False)(encoder)
encoder = BatchNormalization(momentum=0.1)(encoder) # enet uses momentum of 0.1, keras default is 0.99
encoder = SpatialDropout2D(dropout_rate)(encoder)
other = inp
# other branch
if downsample:
other = MaxPooling2D()(other)
other = Permute((1, 3, 2))(other)
pad_feature_maps = output - inp.get_shape().as_list()[3]
tb_pad = (0, 0)
lr_pad = (0, pad_feature_maps)
other = ZeroPadding2D(padding=(tb_pad, lr_pad))(other)
other = Permute((1, 3, 2))(other)
encoder = add([encoder, other])
encoder = PReLU(shared_axes=[1, 2])(encoder)
return encoder
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