Abstract
This paper concerns the problem of wood cellular structure image registration. Given the large variability of wood geometry and the important changes in the cellular organization due to moisture sorption, an affine-based image registration technique is not exhaustive to describe the overall hygro-mechanical behaviour of wood at micrometre scales. Additionally, free tools currently available for non-rigid image registration are not suitable for quantifying the structural deformations of complex hierarchical materials such as wood, leading to errors due to misalignment. In this paper, we adapt an existing non-rigid registration model based on B-spline functions to our case study. The so-modified algorithm combines the concept of feature recognition within specific regions locally distributed in the material with an optimization problem. Results show that the method is able to quantify local deformations induced by moisture changes in tomographic images of wood cell wall with high accuracy. The local deformations provide new important insights in characterizing the swelling behaviour of wood at the cell wall level.
Highlights
Wood, a cellular biological material, swells or shrinks due to the adsorption or desorption of water in the hygroscopic domain
This paper presents a quantitative approach to precisely capture the local deformations of wood cellular structure in highresolution tomographic datasets
Wood swells when exposed to an increase in relative humidity (RH) and the typical deformations observed in the cellular structure of wood samples has been described globally
Summary
A cellular biological material, swells or shrinks due to the adsorption or desorption of water in the hygroscopic domain. While sorption occurs within the cell wall material, the cellular organization of wood leads to significant deformations in the transversal directions of wood, i.e. tangentially and radially to the growth rings, with very little swelling in the longitudinal direction. The tracheids, are vertical in the trunk but 5–10% of the cells, named rays, are positioned horizontally linking radially the cells across growth rings. Given this geometrical variability, an analysis of wood deformations at the cellular scale could elucidate whether swelling is regular. To allow introducing the basic idea of the new algorithm, aimed at capturing the local deformations of cellular materials, such as wood, a general mathematical description of image registration method is first given
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