First, a CNN is not one process. It's actually a complex network of interconnected processes, organized in layers. With each layer, the CNN can detect higher-level, more abstract features. When the CNN is identifying these features, it uses something called a filter. Here's how Larry Carin, one of the authors of a JAMA Guide to Statistics and Methods article on CNNs, describes a filter: So, we think about a medical image, a medical image in radiology or ophthalmology or dermatology is characterized by local structure,