The present invention relates to apparatus (10) for determining a respiration volume signal from a subject (12), comprising a processing unit (28) for receiving image data (26) detected from a field of view (42) and for determining an alternating signal (S) including vital sign information (R) of the subject (12) from the image data (26), an analysis unit (30) for determining at least one characteristic parameter (A) corresponding to a respiration parameter of the subject (12) on the basis of the alternating signal (S), a calibration unit (32) for determining a calibration value (V1, V2) on the basis of a breathing volume measured during inhale and/or exhale of the subject (12) by means of an airflow or an air volume measurement, and a calculation unit (34) for calculating the respiration volume of the subject (12) on the basis of the calibration value (V1, V2) and the at least one characteristic parameter (A).
