A fragmenting rotor assembly for comminuting waste wood and other fragmentable material. The marker comprises an oligopeptide covalently labelled with a fluorescent dye and is characterised in that the dye has a net charge that will maintain the overall net charge of the oligopeptide upon being bound to the oligopeptide. The connector pin 8 is arranged rotatably relative to both of the outboard bushings 6 and the inboard bushings 7, and the flange portions 9 are arranged slidably relative to outboard end faces 6b of the corresponding outboard bushings 6 without being prevented from rotation relative to the boom 4. Clip detection logic is provided to detect clipping at the output of the channel, preferably by detecting successive edges of the reference waveform without an intervening edge of a PWM output signal. An intrinsic color of a given pixel located in an area of interest that is adjacent to at least one of the first and second regions is estimated by extrapolating from colors of multiple pixels in one of the first and second regions and multiple pixels in the other of the two regions.