Image based methods for nondestructive detection of compression wood in sawn timber

Sammanfattning: Compression wood is an anomaly in wood formed by the living softwood tree to compensate for excessive, asymmetric loads by developing special fibres. Compression wood has special properties that are unwanted in the utilisation of sawn wood products and is thus desirable to detect and reject in an early stage. It is difficult to detect manually and there are no commonly used nondestructive methods for automatic detection of compression wood today. This thesis is based on work reported in four papers that describe development, evaluation and comparison of four different methods for nondestructive detection of compression wood. Spectral and colour scanning both utilises differences in the spectral composition of light reflected from the wood surface to bring out contrast between normal wood and compression wood. X-ray scanning detects radiation transmitted through the wood. Absorption of x-rays is closely related to the density, which is higher for compression wood than normal wood. Tracheid-effect scanning utilises the direction oriented light-scattering properties of wood fibres, which is less pronounced in compression wood. The methods have been developed and evaluated using material with biological variations and different moisture content. Classification of compression wood in real-time is considered and discussed, with industrial implementation of the methods in mind.