Collection area for gamma rays, expressed as a function of the true energy. Black lines: Cloudless condition (T1). Blue: cloudy data analysed with cloudless MC simulations. Green: Cloud analysed with dedicated MC simulations. Red: image-correction method analysed with general cloudless MC simulations. Dashed lines show the results with an additional cleaning (AC). Different panels show different transmission, T, and base height, h, of the cloud. Efficiency cuts in gammaness (90%) and θ² (70%) are applied. The second and fourth rows of subpanels show selected ratios of the collection areas shown in the first and third rows (see legend).