def residual_block(x,
in_filter,
out_filter,
stride,
update_bn=True,
activate_before_residual=False):
"""Adds residual connection to `x` in addition to applying BN->ReLU->3x3 Conv.
Args:
x: Tensor that is the output of the previous layer in the model.
in_filter: Number of filters `x` has.
out_filter: Number of filters that the output of this layer will have.
stride: Integer that specified what stride should be applied to `x`.
activate_before_residual: Boolean on whether a BN->ReLU should be applied
to x before the convolution is applied.
Returns:
A Tensor that is the result of applying two sequences of BN->ReLU->3x3 Conv
and then adding that Tensor to `x`.
"""
if activate_before_residual: # Pass up RELU and BN activation for resnet
with tf.variable_scope('shared_activation'):
x = ops.batch_norm(x, update_stats=update_bn, scope='init_bn')
x = tf.nn.relu(x)
orig_x = x
else:
orig_x = x
block_x = x
if not activate_before_residual:
with tf.variable_scope('residual_only_activation'):
block_x = ops.batch_norm(block_x,
update_stats=update_bn,
scope='init_bn')
block_x = tf.nn.relu(block_x)
with tf.variable_scope('sub1'):
block_x = ops.conv2d(block_x,
out_filter,
3,
stride=stride,
scope='conv1')
with tf.variable_scope('sub2'):
block_x = ops.batch_norm(block_x, update_stats=update_bn, scope='bn2')
block_x = tf.nn.relu(block_x)
block_x = ops.conv2d(block_x, out_filter, 3, stride=1, scope='conv2')
with tf.variable_scope(
'sub_add'): # If number of filters do not agree then zero pad them
if in_filter != out_filter:
orig_x = ops.avg_pool(orig_x, stride, stride)
orig_x = ops.zero_pad(orig_x, in_filter, out_filter)
x = orig_x + block_x
return x
def shortcut(x, output_filters, stride):
"""Applies strided avg pool or zero padding to make output_filters match x."""
num_filters = int(x.shape[3])
if stride == 2:
x = ops.avg_pool(x, 2, stride=stride, padding='SAME')
if num_filters != output_filters:
diff = output_filters - num_filters
assert diff > 0
# Zero padd diff zeros
padding = [[0, 0], [0, 0], [0, 0], [0, diff]]
x = tf.pad(x, padding)
return x
def _res_add(in_filter, out_filter, stride, x, orig_x):
"""Adds `x` with `orig_x`, both of which are layers in the model.
Args:
in_filter: Number of filters in `orig_x`.
out_filter: Number of filters in `x`.
stride: Integer specifying the stide that should be applied `orig_x`.
x: Tensor that is the output of the previous layer.
orig_x: Tensor that is the output of an earlier layer in the network.
Returns:
A Tensor that is the result of `x` and `orig_x` being added after
zero padding and striding are applied to `orig_x` to get the shapes
to match.
"""
if in_filter != out_filter:
orig_x = ops.avg_pool(orig_x, stride, stride)
orig_x = ops.zero_pad(orig_x, in_filter, out_filter)
x = x + orig_x
orig_x = x
return x, orig_x