A convolutional neural network processes structured grids such as images by learning local patterns and combining them into increasingly complex representations. Unlike a fully connected layer, each output uses a small neighborhood of inputs, while shared weights slide across the whole image. This reduces parameters and applies the same feature detector everywhere. section 10.0
The hierarchy moves from simple visual properties to larger structures: lower layers can detect edges and corners, later layers can combine them into ears, eyes, and noses, and still higher layers can recognize faces. Pooling summarizes local patches and downsamples feature maps, making small positional changes less consequential. section 10.0 section 10.7
From local patches to image understanding
A convolutional filter can detect an edge throughout an image because its weights are shared. A later layer combines detected edges into parts such as eyes or noses, while pooling with a 2 × 2 kernel and stride 2 reduces each feature map to half its width and height. These representations support image classification and, when locations are also predicted with bounding boxes, object detection. section 10.0 section 10.7 section 11.0
Figure 10.19 Max pooling using a 2 × 2 kernel with stride 2. The resulting output feature map is half the size of the input feature map. Each value of the output feature map is a max of the corresponding local patch in the input feature map.
A pooling diagram shows how each 2 × 2 input patch becomes one maximum value and how the output feature map is reduced. section 10.7

















