  The CoRoT space mission was operating for almost 6 years, producing thousands
of continuous photometric light curves. The temporal series of exposures are
processed by the production pipeline, correcting the data for known
instrumental effects. But even after these model-based corrections, some
collective trends are still visible in the light curves. We propose here a
simple exposure-based algorithm to remove instrumental effects. The effect of
each exposure is a function of only two instrumental stellar parameters,
position on the CCD and photometric aperture. The effect is not a function of
the stellar flux, and therefore much more robust. As an example, we show that
the $\sim2\%$ long-term variation of the early run LRc01 is nicely detrended on
average. This systematics removal process is part of the CoRoT legacy data
pipeline.
