Optimal filters for a exponential source in a background ﹩P( q) =Dq^{-\gamma }﹩ for ﹩\gamma =0﹩ (white noise, solid line), ﹩\gamma =1﹩ (﹩1/ f﹩ noise, dotted line), ﹩\gamma =2﹩ (short‐dashed line), and ﹩\gamma =3﹩ (long‐dashed line). One‐, two‐, and three‐dimensional cases are represented. There is a degeneration in the case ﹩n=3﹩, where the ﹩\gamma =0﹩ line overlaps with the ﹩\gamma =2﹩ one.