A device and method for reliably and accurately obtaining respiratory information of a subject despite motion of the subject are disclosed. The proposed device comprises a motion signal computing unit for computing a number M of motion signals for a plurality of pixels and/or groups of pixels of at least a region of interest for a number N of image frames of a subject, a transformation unit for computing, for some or all M motion signals, a number of source signals representing independent motions within said images by applying a transformation to the respective motion signals to obtain source signals representing independent motions within said N image frames, and a selection unit for selecting a source signal from among said computed source signals representing respiration of said subject by examining one or more properties of said source signals for some or all of said computed source signals.
