Histogram of the measured values of A_obs = Q₁₁ + Q₂₂ from simulations of the CTI effect, as a function of the object signal-to-noise ratio. The logarithmic grey scale and white contours (enclosing 68.3%, 95.45%, and 99.73% of samples, respectively) show the 10⁷ exponential disk galaxies analysed in I15. Input simulations containing Poisson distributed sky noise were subjected to CTI and Gaussian read-out noise. Then, the CTI was removed using the correct trap model. Dashed and dot-dashed contours (both smoothed) enclose the same density levels measured from 10⁵ simulations with ~35% (~85%) higher signal-to-noise. In all three cases, the noise causes a non-negligible fraction of the galaxies to be measured with A_obs< 0.