What does global pooling do?

Question

I recently found the "global_pooling" flag in the Pooling layer in caffe, however was unable to find sth about it in the documentation here (Layer Catalogue) nor here (Pooling doxygen doc) .

Is there an easy forward examply explanation to this in comparison to the normal Pool-Layer behaviour?

Answer 1

With Global pooling reduces the dimensionality from 3D to 1D. Therefore Global pooling outputs 1 response for every feature map. This can be the maximum or the average or whatever other pooling operation you use.

It is often used at the end of the backend of a convolutional neural network to get a shape that works with dense layers. Therefore no flatten has to be applied.