Heartwood detection in Scots pine by means of heat-sensitive infrared images

Automatic heartwood detection will improve the ability to produce timber of prescribed properties and increase sawmill revenues. In fresh crosscuts, evaporation cools the surface more in the moist sapwood than in the drier heartwood areas. In this semi-industrial investigation, infrared exposures of 180 pine sawlogs were analysed. An algorithm was established to determine the heartwood diameter fraction in a digital temperature profile through the crosscut. Top end heartwood diameter could then be computed automatically by multiplying top end diameter (measured by a traditional log scanner) with the heartwood fraction calculated from an infrared exposure taken at an arbitrary end. The temperature gradient between the heart- and sapwood indicated the accuracy of the method. A promising application would be to use the heartwood fraction to estimate mean annual ring width and other related wood properties, and to use the temperature gradient to indicate the log freshness.