Robustness of RIS with respect to the reconstruction method applied to generate the triggering image and on the triggering energy. Left panel: χ² values at different energies when the triggering image is reconstrcuted by means of MEM_GE (black), forward-fit with PSO (red) and CLEAN (green). The χ² values provided by MEM_GE independently at each energy channel are shown in blue. Right panel: χ² values at different energies when the triggering energy corresponds to the lowest channel and the regularization process flows from low to high energies (black), the triggering energy corresponds to the highest channel and the regularization process flows from high to low energies (red), and the triggering energy has an intermediate value with the regularization process flowing along both directions (green).