Performance of the improvement criterion for pixel selection over the default selection method for near-caustic sources. The number of candidate solutions selected for the zoom at each iteration by the default-solving algorithm (gray diamonds) and by the improvement criterion (red triangles) for the elliptical galaxy of Fig. 3 when the source approaches the caustics. The improvement criterion controls the number of tiles to iterate over and recovers the five macroimages in seven iterations, whereas the standard selection routine identifies an ever-increasing number of pixels, which selects more than 10⁵ tiles for the zoom at the eighth iteration.