The present invention relates to calibration in X ray phase contrast imaging. In order to remove the disturbance due to individual gain factors a calibration filter grating (10) for a slit scanning X ray phase contrast imaging arrangement is provided that comprises a first plurality of filter segments (11) comprising a filter material (12) and a second plurality of opening segments (13). The filter segments and the opening segments are arranged alternating as a filter pattern (15). The filter material is made from a material with structural elements (14) comprising structural parameters in the micrometer region. The filter grating is movably arranged between an X ray source grating (54) and an analyzer grating (60) of an interferometer unit in a slit scanning system of a phase contrast imaging arrangement. The slit scanning system is provided with a pre collimator (55) comprising a plurality of bars (57) and slits (59). The filter pattern is aligned with the pre collimator pattern (61).
