Light curve extracted from a CHEOPSim image time series, using photometric extraction performed by the data reduction pipeline that will be used with real CHEOPS data, for planet HD 80606b (radius 0.987R_J, orbital period 111 days), orbiting the star HD80606 (V = 9.00, spectral type G5V). The exposure duration is 7 s and the exposures are stacked with stacking order 5. Gaps in the light curve correspond to interruptions due to Earth occultation (once per CHEOPS orbit). The simulated photon flux from the target star incident on the telescope, with stellar granulation as the only noise source, is shown by the red line. The transit depth from the photometric extraction is diluted by factor 2 due to the presence of the binary companion star HD 80607 within the photometric aperture (radius 33 pixels), visible in the example image shown on the right. The sawtooth pattern is due to variation of the fraction of the irregularly shaped PSF of the companion star which lies within the circular photometric aperture as the field of view rotates. The pale blue-grey points show the light curve from the same image data, using a larger photometric aperture radius of 92.3 pixels, such that the all the flux from both stars is fully contained. In this case, the sawtooth pattern is absent.