Imaging method and metrology device

Disclosed is an imaging method comprising obtaining a set of primary deconvolution kernels or a set of impulse responses relating to an optical system used to capture said image; obtaining said image signal, said image signal being subject to one or more imaging effects including at least one or more non-isoplanatic imaging effects; performing a low-rank approximation on said set of primary deconvolution kernels or impulse responses to determine respectively a set of deconvolution modes or a set of impulse response modes, each deconvolution mode comprising a modal secondary deconvolution kernel and a modal weight function and each impulse response mode comprising a modal impulse response and a modal inverse weight function; obtaining at least approximated imaging effect-free object information related to said object by applying said modal secondary deconvolution kernels and modal weight functions or said modal impulse responses and modal inverse weight functions to said image signal.