Different methods of background modelling, illustrated in the example of an observation of the η Carinae region (obs. id. 0112560101). The panels include a three-band false-colour image of the EPIC observation (0.2−1.0 keV, 1.0−2.0 keV, 2.0−12.0 keV), showing the complex background structure of the field (panel a), the MOS1 background map derived from a spline fit (panel b) and from adaptive smoothing (panel c), the source-excised image (panel e), its ratio to the two background maps (panels f and g) and the ratio between them (panel h). The source-excised image is smoothed with a Gaussian kernel of increasing width (panel i). All images have a linear intensity scale. The smoothed layers which are chosen per image pixel to construct the background map according to their S/N are shown in grey-scale (panel d).