Examples of imaging residuals, convergence, and residual source surface brightness for one mock lens system based on B1608+656 (top row) and PG1115+080 (bottom row). The far left panel shows the gravitational imaging residuals when only an elliptical Sérsic profile, the same profile used to create the mock data, is used to model the background source. The second from left panel shows the imaging residuals when shapelets are added to the source light profile. The dark matter halos that perturb the lensed arc in the mock data are shown in the third from left panel, and the residual source surface brightness is shown in the far right panel.