Particle size measurement on the board surface
If the particle contingent cannot first be prepared and the outlay regarding the image acquisition needs to be minimised, complex image processing methods must be implemented. For scenes with non-isolated particles, the advanced layer analysis (see literature) is suitable. This treats the grey-scale images like a “grey-scale mountain range” and can restore particle contours. A particle size measurement directly on the board surface is, with certain restrictions, thereby possible.
The illustration top left shows a section of the surface of a laboratory worktop taken using a flatbed scanner; top right is the detection result. A sample of the un-pressed surface layer particles was additionally photographed and measured using the FibreShape device, whereby the fine material was sieved out in advance. The 1200dpi photos of the particle contours were then also divided into smaller parts and measured using standard methods. For both evaluations, particles with an area smaller than 0.5mm² and with form factors which indicated an irregular particle shape were not taken into account.
The measured distribution of particle length data was very similar for the two different methods. The proportion of longer particles is slightly higher for the individual measurement, but the modal values correspond entirely. When particle board surfaces are assessed, the “fine-particleness” also plays a role, i.e. the emergence of loose particles or other conspicuously large particles. This proportion is found in both distributions for particle lengths from around 5mm and can be assessed using e.g. the quantile.
Fraunhofer Institute for Wood Research 
