An Automatic Tree Ring Measurement System

This paper describes a robust and portable tree ring parameter measurement system, which has a potential of surpassing state-of-the-art systems. A radially movable hand-held scanner is utilized. The problem of different vertical resolution in the image is handled using vertically adaptive filters in the subimages. A two-step segmentation strategy is taken. The periodicity of tree rings is first estimated in each subimage using the "Gray Level Gap Length" method. Then the result serves as input parameter in the succeeding processes. Scanning and processing the same tree sector 25 times, error analysis shows that the system gives reproducible results. Comparison to manual measurements shows that the system is quite reliable. The robustness of the system has also been demonstrated by measuring different types of trees. which is portable, robust and, nevertheless, precise. Our system utilizes a PC and a radially movable hand-hold scanner. The centre of the scanning circle is placed at the pith while scanning on a cross section of a log. It measures a whole tree sector instead of scanning along a tree diameter as one usually does. The resolution is also quite high, 400 dpi. A polar-to-cartesian coordinate transform is performed automatically by the scanner, such that circular tree rings appear as vertical stripes in the image. This texture feature is first extracted as a kind of self-learning process. The knowledge is utilized to control other parameters in the succeeding processes. A simple scheme in Figure 1 describes the strategies of the system. In the output, each tree ring is characterized in terms of its position, and the width of its earlywood and latewood portions. A number of parameters are Introduction acqulcltlon Tree rings of evergreens are an important feature which characterizes the biological and physical properties of trees. They also reflect the environmental conditions in the growing season. A tree ring is normally composed of an earlywood and a latewood portion. Earlywood fibres have a larger volume, thinner fibre-wall, and lighter colour compared to latewood fibres. Their bonding and strength properties are also different. Tree ring measurement has gain an increasing interest in forest research, wood technology, dendrochronology, dendroclimatology, and pulp and paper industry. Existing measurement systems for automatic tree ring registration are mainly based on optical cameras (11 [21 [3]. Insufficient resolution of the cameras are the main problem which reduce the efficiency of such systems. So, the measurements are often rough estimations in some specific areas, or are registered only according to 1 or 2 radii along the scanning direction. The width of the earlywoodllatewood portion is usually not measured. We present a new tree ring measurement system Segmentat~on and