Keras中的特征缩放和移位（FiLM层）
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我试图将特征方式的缩放和移位（也称为仿射变换 - 这个想法在this distill article的命名法部分中描述）应用于Keras张量（具有TF后端）。
我想要变换的张量，称为X，是卷积层的输出，并且具有形状(B,H,W,F)，表示（批量大小，高度，宽度，特征映射的数量）。
我的变换参数是两个(B,F)维张量，beta和gamma。
我想要X * gamma + beta，或者更具体，
for b in range(B):
for f in range(F):
X[b,:,:,f] = X[b,:,:,f] * gamma[b,f] + beta[b,f]
然而，这两种方式都不适用于Keras。第二个是元素分配，由于失败而失败
TypeError: 'Tensor' object does not support item assignment
并且应该是相当低效的。
第一次失败对我来说更加神秘，但我的猜测是广播问题。在下面的完整代码+追溯中，您可以看到我的尝试。
需要注意的两点是错误只发生在训练时（而不是编译时），并且'transform_vars'输入似乎从未使用过，至少根据模型摘要。
有关如何实现这一点的任何想法？
import numpy as np
import keras as ks
import keras.backend as K
print(ks.__version__)
# Load example data (here MNIST)
from keras.datasets import mnist
(x_img_train, y_train), _ = mnist.load_data()
x_img_train = np.expand_dims(x_img_train,-1)
# Generator some data to use for transformations
n_transform_vars = 10
x_transform_train = np.random.randn(y_train.shape[0], n_transform_vars)
# Inputs
input_transform = ks.layers.Input(x_transform_train.shape[1:], name='transform_vars')
input_img = ks.layers.Input(x_img_train.shape[1:], name='imgs')
# Number of feature maps
n_features = 32
# Create network that calculates the transformations
tns_transform = ks.layers.Dense(2 * n_features)(input_transform)
tns_transform = ks.layers.Reshape((2, 32))(tns_transform)
# Do a convolution
tns_conv = ks.layers.Conv2D(filters=n_features, kernel_size=3, padding='same')(input_img)
# Apply batch norm
bn = ks.layers.BatchNormalization()
# Freeze the weights of the batch norm, as they are going to be overwritten
bn.trainable = False
# Apply
tns_conv = bn(tns_conv)
# Attempt to apply the affine transformation
def scale_and_shift(x):
return x * tns_transform[:,0] + tns_transform[:,1]
tns_conv = ks.layers.Lambda(scale_and_shift, name='affine_transform')(tns_conv)
tns_conv = ks.layers.Flatten()(tns_conv)
output = ks.layers.Dense(1)(tns_conv)
model = ks.models.Model(inputs=[input_img, input_transform], outputs=output)
model.compile(loss='mse', optimizer='Adam')
model.summary()
model.fit([x_img_train, x_transform_train], y_train, batch_size=8)
这导致了
2.2.4
_________________________________________________________________
Layer (type) Output Shape Param #
=================================================================
imgs (InputLayer) (None, 28, 28, 1) 0
_________________________________________________________________
conv2d_25 (Conv2D) (None, 28, 28, 32) 320
_________________________________________________________________
batch_normalization_22 (Batc (None, 28, 28, 32) 128
_________________________________________________________________
affine_transform (Lambda) (None, 28, 28, 32) 0
_________________________________________________________________
flatten_6 (Flatten) (None, 25088) 0
_________________________________________________________________
dense_33 (Dense) (None, 1) 25089
=================================================================
Total params: 25,537
Trainable params: 25,409
Non-trainable params: 128
_________________________________________________________________
Epoch 1/1
---------------------------------------------------------------------------
InvalidArgumentError Traceback (most recent call last)
<ipython-input-35-14724d9432ef> in <module>
49 model.summary()
50
---> 51 model.fit([x_img_train, x_transform_train], y_train, batch_size=8)
~/miniconda3/envs/py3/lib/python3.6/site-packages/keras/engine/training.py in fit(self, x, y, batch_size, epochs, verbose, callbacks, validation_split, validation_data, shuffle, class_weight, sample_weight, initial_epoch, steps_per_epoch, validation_steps, **kwargs)
1037 initial_epoch=initial_epoch,
1038 steps_per_epoch=steps_per_epoch,
-> 1039 validation_steps=validation_steps)
1040
1041 def evaluate(self, x=None, y=None,
~/miniconda3/envs/py3/lib/python3.6/site-packages/keras/engine/training_arrays.py in fit_loop(model, f, ins, out_labels, batch_size, epochs, verbose, callbacks, val_f, val_ins, shuffle, callback_metrics, initial_epoch, steps_per_epoch, validation_steps)
197 ins_batch[i] = ins_batch[i].toarray()
198
--> 199 outs = f(ins_batch)
200 outs = to_list(outs)
201 for l, o in zip(out_labels, outs):
~/miniconda3/envs/py3/lib/python3.6/site-packages/keras/backend/tensorflow_backend.py in __call__(self, inputs)
2713 return self._legacy_call(inputs)
2714
-> 2715 return self._call(inputs)
2716 else:
2717 if py_any(is_tensor(x) for x in inputs):
~/miniconda3/envs/py3/lib/python3.6/site-packages/keras/backend/tensorflow_backend.py in _call(self, inputs)
2673 fetched = self._callable_fn(*array_vals, run_metadata=self.run_metadata)
2674 else:
-> 2675 fetched = self._callable_fn(*array_vals)
2676 return fetched[:len(self.outputs)]
2677
~/miniconda3/envs/py3/lib/python3.6/site-packages/tensorflow/python/client/session.py in __call__(self, *args, **kwargs)
1437 ret = tf_session.TF_SessionRunCallable(
1438 self._session._session, self._handle, args, status,
-> 1439 run_metadata_ptr)
1440 if run_metadata:
1441 proto_data = tf_session.TF_GetBuffer(run_metadata_ptr)
~/miniconda3/envs/py3/lib/python3.6/site-packages/tensorflow/python/framework/errors_impl.py in __exit__(self, type_arg, value_arg, traceback_arg)
526 None, None,
527 compat.as_text(c_api.TF_Message(self.status.status)),
--> 528 c_api.TF_GetCode(self.status.status))
529 # Delete the underlying status object from memory otherwise it stays alive
530 # as there is a reference to status from this from the traceback due to
InvalidArgumentError: Incompatible shapes: [8,28,28,32] vs. [8,32]
[[{{node training_5/Adam/gradients/affine_transform_18/mul_grad/BroadcastGradientArgs}} = BroadcastGradientArgs[T=DT_INT32, _class=["loc:@training_5/Adam/gradients/batch_normalization_22/cond/Merge_grad/cond_grad"], _device="/job:localhost/replica:0/task:0/device:CPU:0"](training_5/Adam/gradients/affine_transform_18/mul_grad/Shape, training_5/Adam/gradients/affine_transform_18/mul_grad/Shape_1)]]
答案
我设法将仿射变换实现为自定义层（此处称为FiLM层，如文献中所示）：
class FiLM(ks.layers.Layer):
def __init__(self, widths=[64,64], activation='leakyrelu',
initialization='glorot_uniform', **kwargs):
self.widths = widths
self.activation = activation
self.initialization = initialization
super(FiLM, self).__init__(**kwargs)
def build(self, input_shape):
assert isinstance(input_shape, list)
feature_map_shape, FiLM_vars_shape = input_shape
self.n_feature_maps = feature_map_shape[-1]
self.height = feature_map_shape[1]
self.width = feature_map_shape[2]
# Collect trainable weights
trainable_weights = []
# Create weights for hidden layers
self.hidden_dense_layers = []
for i,width in enumerate(self.widths):
dense = ks.layers.Dense(width,
kernel_initializer=self.initialization,
name=f'FiLM_dense_{i}')
if i==0:
build_shape = FiLM_vars_shape[:2]
else:
build_shape = (None,self.widths[i-1])
dense.build(build_shape)
trainable_weights += dense.trainable_weights
self.hidden_dense_layers.append(dense)
# Create weights for output layer
self.output_dense = ks.layers.Dense(2 * self.n_feature_maps, # assumes channel_last
kernel_initializer=self.initialization,
name=f'FiLM_dense_output')
self.output_dense.build((None,self.widths[-1]))
trainable_weights += self.output_dense.trainable_weights
# Pass on all collected trainable weights
self._trainable_weights = trainable_weights
super(FiLM, self).build(input_shape)
def call(self, x):
assert isinstance(x, list)
conv_output, FiLM_vars = x
# Generate FiLM outputs
tns = FiLM_vars
for i in range(len(self.widths)):
tns = self.hidden_dense_layers[i](tns)
tns = get_activation(activation=self.activation)(tns)
FiLM_output = self.output_dense(tns)
# Duplicate in order to apply to entire feature maps
# Taken from https://github.com/GuessWhatGame/neural_toolbox/blob/master/film_layer.py
FiLM_output = K.expand_dims(FiLM_output, axis=[1])
FiLM_output = K.expand_dims(FiLM_output, axis=[1])
FiLM_output = K.tile(FiLM_output, [1, self.height, self.width, 1])
# Split into gammas and betas
gammas = FiLM_output[:, :, :, :self.n_feature_maps]
betas = FiLM_output[:, :, :, self.n_feature_maps:]
# Apply affine transformation
return (1 + gammas) * conv_output + betas
def compute_output_shape(self, input_shape):
assert isinstance(input_shape, list)
return input_shape[0]
它取决于函数get_activation，它基本上只返回一个Keras激活实例。您可以在下面看到完整的工作示例。
请注意，此图层在图层本身中处理transform_vars。如果要在其他网络中处理这些变量，请参阅下面的编辑。
import numpy as np
import keras as ks
import keras.backend as K
def get_activation(tns=None, activation='relu'):
'''
Adds an activation layer to a graph.
Args :
tns :
*Keras tensor or None*
Input tensor. If not None, then the graph will be connected through
it, and a tensor will be returned. If None, the activation layer
will be returned.
activation :
*str, optional (default='relu')*
The name of an activation function.
One of 'relu', 'leakyrelu', 'prelu', 'elu', 'mrelu' or 'swish',
or anything that Keras will recognize as an activation function
name.
Returns :
*Keras tensor or layer instance* (see tns argument)
'''
if activation == 'relu':
act = ks.layers.ReLU()
elif activation == 'leakyrelu':
act = ks.layers.LeakyReLU()
elif activation == 'prelu':
act = ks.layers.PReLU()
elif activation == 'elu':
act = ks.layers.ELU()
elif activation == 'swish':
def swish(x):
return K.sigmoid(x) * x
act = ks.layers.Activation(swish)
elif activation == 'mrelu':
def mrelu(x):
return K.minimum(K.maximum(1-x, 0), K.maximum(1+x, 0))
act = ks.layers.Activation(mrelu)
elif activation == 'gaussian':
def gaussian(x):
return K.exp(-x**2)
act = ks.layers.Activation(gaussian)
elif activation == 'flipped_gaussian':
def flipped_gaussian(x):
return 1 - K.exp(-x**2)
act = ks.layers.Activation(flipped_gaussian)
else:
act = ks.layers.Activation(activation)
if tns is not None:
return act(tns)
else:
return act
class FiLM(ks.layers.Layer):
def __init__(self, widths=[64,64], activation='leakyrelu',
initialization='glorot_uniform', **kwargs):
self.widths = widths
self.activation = activation
self.initialization = initialization
super(FiLM, self).__init__(**kwargs)
def build(self, input_shape):
assert isinstance(input_shape, list)
feature_map_shape, FiLM_vars_shape = input_shape
self.n_feature_maps = feature_map_shape[-1]
self.height = feature_map_shape[1]
self.width = feature_map_shape[2]
# Collect trainable weights
trainable_weights = []
# Create weights for hidden layers
self.hidden_dense_layers = []
for i,width in enumerate(self.widths):
dense = ks.layers.Dense(width,
kernel_initializer=self.initialization,
name=f'FiLM_dense_{i}')
if i==0:
build_shape = FiLM_vars_shape[:2]
else:
build_shape = (None,self.widths[i-1])
dense.build(build_shape)
trainable_weights += dense.trainable_weights
self.hidden_dense_layers.append(dense)
# Create weights for output layer
self.output_dense = ks.layers.Dense(2 * self.n_feature_maps, # assumes channel_last
kernel_initializer=self.initialization,
name=f'FiLM_dense_output')
self.output_dense.build((None,self.widths[-1]))
trainable_weights += self.output_dense.trainable_weights
# Pass on all collected trainable weights
self._trainable_weights = trainable_weights
super(FiLM, self).build(input_shape)
def call(self, x):
assert isinstance(x, list)
conv_output, FiLM_vars = x
# Generate FiLM outputs
tns = FiLM_vars
for i in range(len(self.widths)):
tns = self.hidden_dense_layers[i](tns)
tns = get_activation(activation=self.activation)(tns)
FiLM_output = self.output_dense(tns)
# Duplicate in order to apply to entire feature maps
# Taken from https://github.com/GuessWhatGame/neural_toolbox/blob/master/film_layer.py
FiLM_output = K.expand_dims(FiLM_output, axis=[1])
FiLM_output = K.expand_dims(FiLM_output, axis=[1])
FiLM_output = K.tile(FiLM_output, [1, self.height, self.width, 1])
# Split into gammas and betas
gammas = FiLM_output[:, :, :, :self.n_feature_maps]
betas = FiLM_output[:, :, :, self.n_feature_maps:]
# Apply affine transformation
return (1 + gammas) * conv_output + betas
def compute_output_shape(self, input_shape):
assert isinstance(input_shape, list)
return input_shape[0]
print(ks.__version__)
# Load example data (here MNIST)
from keras.datasets import mnist
(x_img_train, y_train), _ = mnist.load_data()
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