根据Keras中共享层的文档,可以创建一个共享层并以不同的输入形状实例化它。文档中给出了一个Conv2D
共享层的例子,如下所示:
a = Input(shape=(32, 32, 3))b = Input(shape=(64, 64, 3))conv = Conv2D(16, (3, 3), padding='same')conved_a = conv(a)# 到目前为止只有一个输入,以下操作有效:assert conv.input_shape == (None, 32, 32, 3)conved_b = conv(b)# 现在`.input_shape`属性将不再工作,但这有效:assert conv.get_input_shape_at(0) == (None, 32, 32, 3)assert conv.get_input_shape_at(1) == (None, 64, 64, 3)
我尝试在Dense
层上做同样的事情,但似乎不起作用。以下是我尝试过的内容,但似乎因为输入形状不匹配而报错。我遗漏了什么吗?
tf.keras.backend.clear_session()dense = Dense(100)i1 = Input(shape=(10,))i2 = Input(shape=(200,))d1 = dense(i1)d2 = dense(i1)d3 = dense(i2)
以下是堆栈跟踪:
---------------------------------------------------------------------------ValueError Traceback (most recent call last)<ipython-input-40-d3fc6212c6ef> in <module>() 5 d1 = dense(i1) 6 d2 = dense(i1)----> 7 d3 = dense(i2)/usr/local/lib/python3.6/dist-packages/tensorflow/python/keras/engine/base_layer.py in __call__(self, inputs, *args, **kwargs) 751 # Check input assumptions set after layer building, e.g. input shape. 752 if build_graph or in_deferred_mode:--> 753 self._assert_input_compatibility(inputs) 754 755 if not in_deferred_mode:/usr/local/lib/python3.6/dist-packages/tensorflow/python/keras/engine/base_layer.py in _assert_input_compatibility(self, inputs) 1511 ' incompatible with the layer: expected axis ' + str(axis) + 1512 ' of input shape to have value ' + str(value) +-> 1513 ' but received input with shape ' + str(shape)) 1514 # Check shape. 1515 if spec.shape is not None:ValueError: Input 0 of layer dense is incompatible with the layer: expected axis -1 of input shape to have value 10 but received input with shape [None, 200]
回答:
当你在这行代码中将dense
层应用于i1
时:
d1 = dense(i1)
这个Dense层的权重会被构建,因此在将来它会期望与其权重兼容形状的输入。这就是为什么在将dense
层应用于i2
后,你会看到以下错误:
expected axis -1 of input shape to have value 10
i1
的形状是(10,)
,因此dense
层会期望形状为(10,)
的样本。但i2
的形状是(200,)
,因此作为dense
层的输入是不兼容的。
卷积层能够应用于具有不同宽度和高度(但具有相同通道数)的输入的原因仅仅是因为它们的权重形状(即卷积核或过滤器)不依赖于输入的空间维度(然而,它依赖于输入的通道数,这就是为什么在你提供的示例中a
和b
都具有3个通道)。