The present invention relates to acquiring reference scan data for X-ray phase-contrast imaging and/or X-ray dark-field imaging. Therefore an X-ray detector (26) is arranged opposite an X-ray source (12) across an examination region (30) with a grating arrangement (18) arranged between the X-ray source (12) and the X-ray detector (26). During an imaging operation without an object in the examination region (30) the grating arrangement (18) is moved in a scanning motion to a number of different positions (a) relative to the X-ray detector (26) whilst the X-ray detector (26) remains stationary relative to the examination region (30) such that in the scanning motion a series of fringe patterns is detected by the X-ray detector (26). The scanning motion is repeated for a different series of fringe patterns. This allows acquiring reference scan data required for calibration of an X-ray imaging device (10′″) with less scanning motions.