1. A method comprising: obtaining representations of an input signal at different lower resolutions, where n denotes a level of spatial resolution, where 0≦n≦N, where level n=N corresponds to the representation having the lowest resolution, where level n=0 corresponds to the input signal, and where the resolution increases as level n decreases; using the n th level representation to estimate and remove low-frequency error from the n−1 th level representation; and then performing application-specific processing on the n−1 th level representation.