The integration of the first 1 Mega-pixel DePFET Sensor with Signal Compression (DSSC) camera, based on the miniaturized silicon drift detector pixel layout (mini-SDD), was completed at the beginning of 2019. The camera is currently installed at the Spectroscopy and Coherent Scattering (SCS) instrument at XFEL where the first user experiment employing the DSSC detector has been conducted at end of May 2019. Calibration of such large-format imager is a complex task due to the large number of gain settings per channel involved, to the peculiar readout architecture and to the minimization of calibration errors required to be compatible with operation at low photon energies (0.5-6 keV). Recently a beam-time dedicated to DSSC camera calibration was conducted at Hera South, DESY, using a unique pulsed X-ray source operating at 4.5 MHz. The results of the preliminary analysis confirm the moderate gain dispersion across each ladder without trimming (i.e. 5%) and an Equivalent Noise Charge of 67±18 electrons r.m.s.. Gain trimming has been conducted on the whole camera showing that gain dispersion after trimming can be successfully kept below 0.68 % r.m.s. (99.6 % of the pixels within ±2 %).