Diaz Giacomo
Department of Biomedical Sciences, University of Cagliari, Cagliari, Italy.
PLoS One. 2017 Dec 8;12(12):e0189427. doi: 10.1371/journal.pone.0189427. eCollection 2017.
The leaf shape is an important taxonomic character. Compared to the classic morphological leaf features such as veins, margin indentations, sinuses, etc., the shape is simpler to obtain by using the 'magic wand' or other contouring tools that are available in most of imaging applications. The only exception is when leaves develop large lobes that get in touch or overlap each other, as the presence of hidden or closed portions of the leaf border precludes the application of automatic methods and forces the leaf contour to be traced manually. This is a time consuming and relatively accurate operation that, nevertheless, can not be avoided, as overlapping lobes are characteristic features of the leaves of several plant species and varieties. The method described in the paper overcomes this problem as it allows the leaf contour to be achieved even in the presence of touching or overlapping lobes. The method involves three steps: (1) the acquisition of leaf images using a transilluminator, (2) a two-level image segmentation that allows all leaf components (blade, overlapping lobes and closed sinuses) to be represented in a single binary image, and (3) the contouring and concatenation of all binary outlines in a single, self-intersecting closed contour that reproduces accurately the leaf shape. The method can be extended to acquire the shape of leaves of herbarium specimens, that are often overlapped but can not be easily handled and repositioned because of their extreme fragility and relevant taxonomic value.
叶片形状是一个重要的分类学特征。与经典的叶片形态特征如叶脉、边缘凹陷、叶缺等相比，通过使用大多数成像应用程序中都有的“魔棒”或其他轮廓工具来获取叶片形状更为简单。唯一的例外是当叶片长出大的裂片并相互接触或重叠时，由于叶片边界存在隐藏或封闭部分，这使得自动方法无法应用，从而必须手动追踪叶片轮廓。这是一项耗时且相对精确的操作，然而却无法避免，因为重叠裂片是几种植物物种和品种叶片的特征。本文所述方法克服了这一问题，因为即使在存在接触或重叠裂片的情况下，它也能实现叶片轮廓的获取。该方法包括三个步骤：（1）使用透照仪获取叶片图像；（2）进行两级图像分割，使所有叶片组件（叶片、重叠裂片和封闭叶缺）都能在单个二值图像中呈现；（3）将所有二值轮廓勾勒并连接成一个单一的、自相交的封闭轮廓，该轮廓能准确再现叶片形状。该方法可以扩展用于获取标本馆标本叶片的形状，这些标本叶片常常相互重叠，并且由于其极度脆弱和重要的分类学价值而不易处理和重新定位。
