The Pooling Layer

A pooling operation makes the space of the height and width smaller. As shown in Figure 7.14, it converts a 2 x 2 area into one element to reduce the space's size:

Figure 7.14: Procedure of max pooling

This example shows this procedure when 2 x 2 max-pooling is conducted with a stride of 2. "Max pooling" takes the maximum value of a region, while "2 x 2" indicates the size of the target region. As we can see, it takes the maximum element in a 2 x 2 region. The stride is 2 in this example, so the 2 x 2 window moves by two elements at one time. Generally, the same value is used for the pooling window size and the stride. For example, the stride is 3 for a 3 x 3 window, and the stride is 4 for a 4 x 4 window.

Note

In addition to max pooling, average pooling can also be used. Max pooling takes the maximum value in the target region, while average pooling averages the values in the target region. In image recognition...