Illustration of the contrast check for mock lenses. Panels (a) and (b) present the deflector and lensed source light, respectively. Panels (c) and (d) show the activated pixels of the deflector and lensed source, respectively. Panel (e) presents the activated pixels of the source, but highlighting in grey the pixels that overlap with the deflector mask. Panel (f) shows all the pixels dominated by the lensed source light, which are used to decide if the mock passes the contrast check. Among them, we highlight in red the pixels that overlap with the deflector, but are still dominated by the lensed source. Lastly, panel (g) shows the final mock lens, which passes the contrast check.