Illustration of the effect of de-noising R on the derivatives of the residual image. From left to right we show a simulated image of a galaxy (Sersic profile) and the three first derivatives of the residual image R in Eq. (19). The first row shows a noise-free image. The second row shows the derivatives of the non-de-noised residuals. The third row shows the derivatives computed using , with a significant improvement of the third derivatives.