目录

Outline

Reduce Dim

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subsample

Max/Avg pooling

  • stride = 2

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Strides

  • stride = 1

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For instance

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import tensorflow as tf
from tensorflow.keras import layers
x = tf.random.normal([1, 14, 14, 4])
x.shape
TensorShape([1, 14, 14, 4])
pool = layers.MaxPool2D(2, strides=2)
out = pool(x)
out.shape
TensorShape([1, 7, 7, 4])
pool = layers.MaxPool2D(3, strides=2)
out = pool(x)
out.shape
TensorShape([1, 6, 6, 4])
out = tf.nn.max_pool2d(x, 2, strides=2, padding='VALID')
out.shape
TensorShape([1, 7, 7, 4])

upsample

  • nearest

  • bilinear

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UpSampling2D

x = tf.random.normal([1, 7, 7, 4])
x.shape
TensorShape([1, 7, 7, 4])
layer = layers.UpSampling2D(size=3)
out = layer(x)
out.shape
TensorShape([1, 21, 21, 4])
layer = layers.UpSampling2D(size=2)
out = layer(x)
out.shape
TensorShape([1, 14, 14, 4])

ReLu

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x = tf.random.normal([2,3])
x
<tf.Tensor: id=76, shape=(2, 3), dtype=float32, numpy=
array([[-0.30181265,  0.39785287, -0.78380096],
       [ 0.6593401 , -0.40962896, -0.3656048 ]], dtype=float32)>
tf.nn.relu(x)
x
<tf.Tensor: id=76, shape=(2, 3), dtype=float32, numpy=
array([[-0.30181265,  0.39785287, -0.78380096],
       [ 0.6593401 , -0.40962896, -0.3656048 ]], dtype=float32)>
layers.ReLU()(x)
<tf.Tensor: id=80, shape=(2, 3), dtype=float32, numpy=
array([[0.        , 0.39785287, 0.        ],
       [0.6593401 , 0.        , 0.        ]], dtype=float32)>
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