This document discusses filtering techniques in the spatial and frequency domains. It describes how a filter H(u,v) is designed and applied to an input signal f(x,y) in the frequency domain to produce an output signal g(x,y). Specifically, it defines ideal low-pass and band-pass filters using a cutoff frequency D0. It also introduces order-statistic (OS) filters which are defined by a set of weighting factors. Finally, it provides an example of applying median and OS filters to a sample image using different padding methods.