Spectral response of Euclid’s wide imaging bands. For comparison we show the Gaia bands that we used – among others – for photometric calibration of the VIS I_E-band, and the atmospheric transmission that limits the ground-based Y, J, H, and K_s bands, for a precipitable water vapour level of 1.0 mm from Rothman et al. (2013). Considerable colour terms may arise for individual sources when transforming fluxes in the wide Euclid bands to fluxes in other photometric systems.