Application of a Wiener filter to the classic “Moon Surface” image on a 2D regular grid with 256 × 256 pixels showing (top, left to right) the original “Moon Surface” signal a), the data including noise b), and the reconstructed map c). The response operator involves a convolution with a Gaussian kernel d) and a masking e). The additive noise is Gaussian white noise with an inhomogeneous standard deviation f) that approximates an overall signal-to-noise ratio ⟨σ_s⟩_Ω/⟨σ_n⟩_Ω of roughly 1. (All figures have been created by NIFTy using the field.plot method.)