# Are noncausal filters ever used in practice?

Basically what it says in the title; I have just started reading about these things and find noncausal filters pretty interesting in concept, but also they do not seem like they would have any advantage worth sacrificing real-time processing. Since "I have just started reading about these things" I feel as if I should make sure, and would also be interested in hearing: does anyone know if there are noncausal filters commonly used in practice? Why are they preferred? Thanks.

Jeff Boucher.

• @PeterK. for the statement system that operates in (near) real time is that you can't look into the future why is that so? Why cant it look into the future by say extrapolation? – GENIVI-LEARNER Mar 24 at 16:11
• @GENIVI-LEARNER Well, there are places where you're effectively doing non-causal filtering, but it's not done in real-time. THe image processing example is the simplest to see: there, the "time" axis is really the $x$ or $y$ axis in the image. The file-on-disk example above also applies: you already have all the data you're going to get, so the filtering operation you're doing can use all of it. Some of it just happens to be "in the future" from your current index into the file. – Peter K. Mar 24 at 20:25