Left: spatial distribution of the four following masks: in red, in orange, in green, and in blue. The percentages in the legend list the fraction of the surface contained in the different masks. Right: flux is integrated over the masks as a function of velocity. The spectrum of different colors shows the evolution of the flux in each line as a function of the mask used: all pixels observed in black, all pixels with in red, in orange, in green, and in blue.