ICL decomposition methods, which are based on SB profile decompositions, are illustrated on the SB profile of the A1668 BCG (black dots). The red shaded region is assigned to the ICL. Method b (left panel) is the SB threshold, in this case at 27 g′ mag arcsec⁻² (horizontal line). All light at fainter SBs is defined as ICL. Method c (middle panel) is the de Vaucouleurs plus excess light decomposition. A de Vaucouleurs profile (black line) is fitted to the inner region (SB < 23 g′ mag arcsec⁻²), and all light above that profile is counted as ICL. Method d (right panel) is the double Sérsic decomposition (two black lines), where all light in the outer Sérsic component (black line above the shaded region) is defined as ICL.