tfmri.layers.AveragePooling2D

class AveragePooling2D(*args, **kwargs)[source]

Bases: keras.layers.pooling.average_pooling2d.AveragePooling2D

Average pooling operation for spatial data.

Note

This layer can be used as a drop-in replacement for tf.keras.layers.AveragePooling2D. However, this one also supports complex-valued pooling. Simply pass dtype='complex64' or dtype='complex128' to the layer constructor.

Downsamples the input along its spatial dimensions (height and width) by taking the average value over an input window (of size defined by pool_size) for each channel of the input. The window is shifted by strides along each dimension.

The resulting output when using "valid" padding option has a shape (number of rows or columns) of: output_shape = math.floor((input_shape - pool_size) / strides) + 1 (when input_shape >= pool_size)

The resulting output shape when using the "same" padding option is: output_shape = math.floor((input_shape - 1) / strides) + 1

For example, for strides=(1, 1) and padding="valid":

>>> x = tf.constant([[1., 2., 3.],
...                  [4., 5., 6.],
...                  [7., 8., 9.]])
>>> x = tf.reshape(x, [1, 3, 3, 1])
>>> avg_pool_2d = tf.keras.layers.AveragePooling2D(pool_size=(2, 2),
...    strides=(1, 1), padding='valid')
>>> avg_pool_2d(x)
<tf.Tensor: shape=(1, 2, 2, 1), dtype=float32, numpy=
  array([[[[3.],
           [4.]],
          [[6.],
           [7.]]]], dtype=float32)>

For example, for stride=(2, 2) and padding="valid":

>>> x = tf.constant([[1., 2., 3., 4.],
...                  [5., 6., 7., 8.],
...                  [9., 10., 11., 12.]])
>>> x = tf.reshape(x, [1, 3, 4, 1])
>>> avg_pool_2d = tf.keras.layers.AveragePooling2D(pool_size=(2, 2),
...    strides=(2, 2), padding='valid')
>>> avg_pool_2d(x)
<tf.Tensor: shape=(1, 1, 2, 1), dtype=float32, numpy=
  array([[[[3.5],
           [5.5]]]], dtype=float32)>

For example, for strides=(1, 1) and padding="same":

>>> x = tf.constant([[1., 2., 3.],
...                  [4., 5., 6.],
...                  [7., 8., 9.]])
>>> x = tf.reshape(x, [1, 3, 3, 1])
>>> avg_pool_2d = tf.keras.layers.AveragePooling2D(pool_size=(2, 2),
...    strides=(1, 1), padding='same')
>>> avg_pool_2d(x)
<tf.Tensor: shape=(1, 3, 3, 1), dtype=float32, numpy=
  array([[[[3.],
           [4.],
           [4.5]],
          [[6.],
           [7.],
           [7.5]],
          [[7.5],
           [8.5],
           [9.]]]], dtype=float32)>
Args:
pool_size: integer or tuple of 2 integers,

factors by which to downscale (vertical, horizontal). (2, 2) will halve the input in both spatial dimension. If only one integer is specified, the same window length will be used for both dimensions.

strides: Integer, tuple of 2 integers, or None.

Strides values. If None, it will default to pool_size.

padding: One of "valid" or "same" (case-insensitive).

"valid" means no padding. "same" results in padding evenly to the left/right or up/down of the input such that output has the same height/width dimension as the input.

data_format: A string,

one of channels_last (default) or channels_first. The ordering of the dimensions in the inputs. channels_last corresponds to inputs with shape (batch, height, width, channels) while channels_first corresponds to inputs with shape (batch, channels, height, width). It defaults to the image_data_format value found in your Keras config file at ~/.keras/keras.json. If you never set it, then it will be “channels_last”.

Input shape:

  • If data_format='channels_last': 4D tensor with shape (batch_size, rows, cols, channels).

  • If data_format='channels_first': 4D tensor with shape (batch_size, channels, rows, cols).

Output shape:

  • If data_format='channels_last': 4D tensor with shape (batch_size, pooled_rows, pooled_cols, channels).

  • If data_format='channels_first': 4D tensor with shape (batch_size, channels, pooled_rows, pooled_cols).

call(inputs)[source]

This is where the layer’s logic lives.

The call() method may not create state (except in its first invocation, wrapping the creation of variables or other resources in tf.init_scope()). It is recommended to create state in __init__(), or the build() method that is called automatically before call() executes the first time.

Parameters

  • inputs –

    Input tensor, or dict/list/tuple of input tensors. The first positional inputs argument is subject to special rules: - inputs must be explicitly passed. A layer cannot have zero

    arguments, and inputs cannot be provided via the default value of a keyword argument.

    • NumPy array or Python scalar values in inputs get cast as tensors.

    • Keras mask metadata is only collected from inputs.

    • Layers are built (build(input_shape) method) using shape info from inputs only.

    • input_spec compatibility is only checked against inputs.

    • Mixed precision input casting is only applied to inputs. If a layer has tensor arguments in *args or **kwargs, their casting behavior in mixed precision should be handled manually.

    • The SavedModel input specification is generated using inputs only.

    • Integration with various ecosystem packages like TFMOT, TFLite, TF.js, etc is only supported for inputs and not for tensors in positional and keyword arguments.

  • *args – Additional positional arguments. May contain tensors, although this is not recommended, for the reasons above.

  • **kwargs –

    Additional keyword arguments. May contain tensors, although this is not recommended, for the reasons above. The following optional keyword arguments are reserved: - training: Boolean scalar tensor of Python boolean indicating

    whether the call is meant for training or inference.

    • mask: Boolean input mask. If the layer’s call() method takes a mask argument, its default value will be set to the mask generated for inputs by the previous layer (if input did come from a layer that generated a corresponding mask, i.e. if it came from a Keras layer with masking support).

Returns

A tensor or list/tuple of tensors.