The DEPFET Sensor with Signal Compression (DSSC) will be a 2d imaging detector for the European X-ray Free Electron Laser (XFEL.EU) currently under construction in Hamburg. In order to reach the anticipated detector performance, a precise knowledge of the Non-Linear System Characteristic (NLSC) of the DSSC is needed. The NLSC describes the relation between the signal charge collected in the internal gate of a DEPFET pixel and the respective digital output. It will have to be calibrated prior to each scientific experiment as a function of the XFEL photon energy and the requested photon counting mode. Moreover, each of the 1024 × 1024 DSSC pixels will have to be calibrated individually due to small pixel-to-pixel variations. We present here an overview of the DSSC calibration procedure, a first experimental calibration of the NLSC of a prototype DSSC pixel as well as a first validation of the calibration.