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deformable_Conv_Layer.py
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deformable_Conv_Layer.py
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import tensorflow as tf
from tensorflow.keras.layers import Conv2D
class DeformableConvLayer(Conv2D):
"""Only support "channel last" data format"""
def __init__(self,
filters,
kernel_size,
strides=(1, 1),
padding='valid',
data_format=None,
dilation_rate=(1, 1),
num_deformable_group=None,
activation=None,
use_bias=True,
kernel_initializer='glorot_uniform',
bias_initializer='zeros',
kernel_regularizer=None,
bias_regularizer=None,
activity_regularizer=None,
kernel_constraint=None,
bias_constraint=None,
**kwargs):
"""`kernel_size`, `strides` and `dilation_rate` must have the same value in both axis.
:param num_deformable_group: split output channels into groups, offset shared in each group. If
this parameter is None, then set num_deformable_group=filters.
"""
super().__init__(
filters=filters,
kernel_size=kernel_size,
strides=strides,
padding=padding,
data_format=data_format,
dilation_rate=dilation_rate,
activation=activation,
use_bias=use_bias,
kernel_initializer=kernel_initializer,
bias_initializer=bias_initializer,
kernel_regularizer=kernel_regularizer,
bias_regularizer=bias_regularizer,
activity_regularizer=activity_regularizer,
kernel_constraint=kernel_constraint,
bias_constraint=bias_constraint,
**kwargs)
self.kernel = None
self.bias = None
self.offset_layer_kernel = None
self.offset_layer_bias = None
if num_deformable_group is None:
num_deformable_group = filters
if filters % num_deformable_group != 0:
raise ValueError('"filters" mod "num_deformable_group" must be zero')
self.num_deformable_group = num_deformable_group
def build(self, input_shape):
input_dim = int(input_shape[-1])
# kernel_shape = self.kernel_size + (input_dim, self.filters)
# we want to use depth-wise conv
kernel_shape = self.kernel_size + (self.filters * input_dim, 1)
self.kernel = self.add_weight(
name='kernel',
shape=kernel_shape,
initializer=self.kernel_initializer,
regularizer=self.kernel_regularizer,
constraint=self.kernel_constraint,
trainable=True,
dtype=self.dtype)
if self.use_bias:
self.bias = self.add_weight(
name='bias',
shape=(self.filters,),
initializer=self.bias_initializer,
regularizer=self.bias_regularizer,
constraint=self.bias_constraint,
trainable=True,
dtype=self.dtype)
# create offset conv layer
offset_num = self.kernel_size[0] * self.kernel_size[1] * self.num_deformable_group
self.offset_layer_kernel = self.add_weight(
name='offset_layer_kernel',
shape=self.kernel_size + (input_dim, offset_num * 2), # 2 means x and y axis
initializer=tf.zeros_initializer(),
regularizer=self.kernel_regularizer,
trainable=True,
dtype=self.dtype)
self.offset_layer_bias = self.add_weight(
name='offset_layer_bias',
shape=(offset_num * 2,),
initializer=tf.zeros_initializer(),
# initializer=tf.random_uniform_initializer(-5, 5),
regularizer=self.bias_regularizer,
trainable=True,
dtype=self.dtype)
self.built = True
def call(self, inputs, training=None, **kwargs):
# get offset, shape [batch_size, out_h, out_w, filter_h, * filter_w * channel_out * 2]
offset = tf.nn.conv2d(inputs,
filter=self.offset_layer_kernel,
strides=[1, *self.strides, 1],
padding=self.padding.upper(),
dilations=[1, *self.dilation_rate, 1])
offset += self.offset_layer_bias
# add padding if needed
inputs = self._pad_input(inputs)
# some length
batch_size = int(inputs.get_shape()[0])
channel_in = int(inputs.get_shape()[-1])
in_h, in_w = [int(i) for i in inputs.get_shape()[1: 3]] # input feature map size
out_h, out_w = [int(i) for i in offset.get_shape()[1: 3]] # output feature map size
filter_h, filter_w = self.kernel_size
# get x, y axis offset
offset = tf.reshape(offset, [batch_size, out_h, out_w, -1, 2])
y_off, x_off = offset[:, :, :, :, 0], offset[:, :, :, :, 1]
# input feature map gird coordinates
y, x = self._get_conv_indices([in_h, in_w])
y, x = [tf.expand_dims(i, axis=-1) for i in [y, x]]
y, x = [tf.tile(i, [batch_size, 1, 1, 1, self.num_deformable_group]) for i in [y, x]]
y, x = [tf.reshape(i, [*i.shape[0: 3], -1]) for i in [y, x]]
y, x = [tf.to_float(i) for i in [y, x]]
# add offset
y, x = y + y_off, x + x_off
y = tf.clip_by_value(y, 0, in_h - 1)
x = tf.clip_by_value(x, 0, in_w - 1)
# get four coordinates of points around (x, y)
y0, x0 = [tf.to_int32(tf.floor(i)) for i in [y, x]]
y1, x1 = y0 + 1, x0 + 1
# clip
y0, y1 = [tf.clip_by_value(i, 0, in_h - 1) for i in [y0, y1]]
x0, x1 = [tf.clip_by_value(i, 0, in_w - 1) for i in [x0, x1]]
# get pixel values
indices = [[y0, x0], [y0, x1], [y1, x0], [y1, x1]]
p0, p1, p2, p3 = [DeformableConvLayer._get_pixel_values_at_point(inputs, i) for i in indices]
# cast to float
x0, x1, y0, y1 = [tf.to_float(i) for i in [x0, x1, y0, y1]]
# weights
w0 = (y1 - y) * (x1 - x)
w1 = (y1 - y) * (x - x0)
w2 = (y - y0) * (x1 - x)
w3 = (y - y0) * (x - x0)
# expand dim for broadcast
w0, w1, w2, w3 = [tf.expand_dims(i, axis=-1) for i in [w0, w1, w2, w3]]
# bilinear interpolation
pixels = tf.add_n([w0 * p0, w1 * p1, w2 * p2, w3 * p3])
# reshape the "big" feature map
pixels = tf.reshape(pixels, [batch_size, out_h, out_w, filter_h, filter_w, self.num_deformable_group, channel_in])
pixels = tf.transpose(pixels, [0, 1, 3, 2, 4, 5, 6])
pixels = tf.reshape(pixels, [batch_size, out_h * filter_h, out_w * filter_w, self.num_deformable_group, channel_in])
# copy channels to same group
feat_in_group = self.filters // self.num_deformable_group
pixels = tf.tile(pixels, [1, 1, 1, 1, feat_in_group])
pixels = tf.reshape(pixels, [batch_size, out_h * filter_h, out_w * filter_w, -1])
# depth-wise conv
out = tf.nn.depthwise_conv2d(pixels, self.kernel, [1, filter_h, filter_w, 1], 'VALID')
# add the output feature maps in the same group
out = tf.reshape(out, [batch_size, out_h, out_w, self.filters, channel_in])
out = tf.reduce_sum(out, axis=-1)
if self.use_bias:
out += self.bias
return self.activation(out)
def _pad_input(self, inputs):
"""Check if input feature map needs padding, because we don't use the standard Conv() function.
:param inputs:
:return: padded input feature map
"""
# When padding is 'same', we should pad the feature map.
# if padding == 'same', output size should be `ceil(input / stride)`
if self.padding == 'same':
in_shape = inputs.get_shape().as_list()[1: 3]
padding_list = []
for i in range(2):
filter_size = self.kernel_size[i]
dilation = self.dilation_rate[i]
dilated_filter_size = filter_size + (filter_size - 1) * (dilation - 1)
same_output = (in_shape[i] + self.strides[i] - 1) // self.strides[i]
valid_output = (in_shape[i] - dilated_filter_size + self.strides[i]) // self.strides[i]
if same_output == valid_output:
padding_list += [0, 0]
else:
p = dilated_filter_size - 1
p_0 = p // 2
padding_list += [p_0, p - p_0]
if sum(padding_list) != 0:
padding = [[0, 0],
[padding_list[0], padding_list[1]], # top, bottom padding
[padding_list[2], padding_list[3]], # left, right padding
[0, 0]]
inputs = tf.pad(inputs, padding)
return inputs
def _get_conv_indices(self, feature_map_size):
"""the x, y coordinates in the window when a filter sliding on the feature map
:param feature_map_size:
:return: y, x with shape [1, out_h, out_w, filter_h * filter_w]
"""
feat_h, feat_w = [int(i) for i in feature_map_size[0: 2]]
x, y = tf.meshgrid(tf.range(feat_w), tf.range(feat_h))
x, y = [tf.reshape(i, [1, *i.get_shape(), 1]) for i in [x, y]] # shape [1, h, w, 1]
x, y = [tf.image.extract_image_patches(i,
[1, *self.kernel_size, 1],
[1, *self.strides, 1],
[1, *self.dilation_rate, 1],
'VALID')
for i in [x, y]] # shape [1, out_h, out_w, filter_h * filter_w]
return y, x
@staticmethod
def _get_pixel_values_at_point(inputs, indices):
"""get pixel values
:param inputs:
:param indices: shape [batch_size, H, W, I], I = filter_h * filter_w * channel_out
:return:
"""
y, x = indices
batch, h, w, n = y.get_shape().as_list()[0: 4]
batch_idx = tf.reshape(tf.range(0, batch), (batch, 1, 1, 1))
b = tf.tile(batch_idx, (1, h, w, n))
pixel_idx = tf.stack([b, y, x], axis=-1)
return tf.gather_nd(inputs, pixel_idx)