Preprocessing steps applied to an image taken on 4 December 2014, cropped around Io. The position of the six-pronged diffraction pattern is denoted by six green lines to aid the eye. It can be seen that the jet becomes more prominent with each step. Panel a: raw image. Panel b: comparison with the other moons. Panel c: removal of the background. Panel d: removal of the vertical saturation pattern. Panel e: reduction of 60° rotational symmetry.