Emission to absorption profile ratio computed using angle-dependent redistribution (black, Eq. (1)), angle-independent redistribution (blue, Eq. (6)) and our intermediate method (red, see Sect. 2) in the observer’s frame as function of reduced frequency q. The cosines of the angle of the ray direction with the coordinate axes (μ_x,μ_y,μ_z) are given in the upper left corner of the panel. The quantity α gives the angle between the gas velocity and the ray direction.