Residuals of CNN measurement on galaxy ellipticities and magnitude. Top panels: the ellipticities’ measurement residuals on 10 000 galaxies of CSST simulations. Colors denote the measured S/N of images, and those with S /N > 50 are shown as the same color as 50. The accuracy sees a strong dependence on the galaxies’ S/N. ρ ≃ 0.98 for S /N > 10 comparing p 0.71 for S/N < 10. Bottom panels: measurement residuals of galaxy magnitude in i band (left) and its histogram of truth and predictions (right). Measurements on faint sources (M_i > 24) are highly biased into being brighter, which propagates into the measured S/N leading to an overestimation.