A colour assessment methodology for oak wood

Context: Customers have limited tolerances for colour differences between oak wood elements in parquetry or furniture, whereas manufacturers are in need of an objective method to communicate possible differences in their products. Aims: This study aimed at grading oak wood boards in objectively defined colour classes in correspondence with the visual assessment by an expert panel. Methods: First the most suitable spectrophotometer for measurements approximating the perception of the human eye was selected. Then three colour grading algorithms were evaluated: one based on the smallest distance towards the centre of the colour subspaces, the second using a classification tree and the last implementing the CIEDE2000 colour difference formula to determine tolerance ellipsoids. Results: Statistical analysis using a classification tree and CIEDE2000 tolerance ellipsoids classified the specimens in good accordance with visual assessment, with a 6% and 5% misclassification respectively. Conclusions: The colour grading methodology can be adapted to particular grading purposes and is proposed as a basis for development of an inline colour grading system to be added to commonly used defect detection scanners