TensorFlow 1.x Deep Learning Cookbook

A mathematical example

One simple way to understand convolution is to think about a sliding window function applied to a matrix. In the following example, given the input matrix I and the kernel K, we get the convolved output. The 3 x 3 kernel K (sometimes called filter or feature detector) is multiplied element-wise with the input matrix to get one cell in the output convolved matrix. All the other cells are obtained by sliding the window on I:

An example of convolutional operation: in bold the cells involved in the computation

In this example, we decided to stop the sliding window as soon as we touch the borders of I (so the output is 3 ...