External labeling deals with annotating features in images with labels that are placed outside of the image and are connected by curves (so-called leaders) to the corresponding features. While external labeling has been extensively investigated from a perspective of automatization, the research on its readability has been neglected. In this article, we present the first formal user study on the readability of leader types in boundary labeling, a special variant of external labeling that considers rectangular image contours. We consider the four most studied leader types (straight, L-shaped, diagonal, and S-shaped) with respect to their performance, that is, whether and how fast a viewer can assign a feature to its label and vice versa. We give a detailed analysis of the results regarding the readability of the four models and discuss their aesthetic qualities based on the users’ preference judgments and interviews. As a consequence of our experiment, we can generally recommend L-shaped leaders as the best compromise between measured task performance and subjective preference ratings, while straight and diagonal leaders received mixed ratings in the two measures. S-shaped leaders are generally not recommended from a practical point of view.

中文翻译：

---

论边界标注中领导者的可读性

外部标签处理使用放置在图像外部并通过曲线（所谓的引线）连接到相应特征的标签来注释图像中的特征。虽然从自动化的角度对外部标签进行了广泛的研究，但对其可读性的研究却被忽视了。在本文中，我们展示了第一个关于边界标记中领导类型可读性的正式用户研究，边界标记是一种考虑矩形图像轮廓的外部标记的特殊变体。我们考虑了四种研究最多的领导者类型（直线型、L 形、对角线和 S 形）的性能，即查看者是否可以以及多快地将特征分配给其标签，反之亦然。我们详细分析了四种模型的可读性结果，并根据用户的偏好判断和访谈讨论了它们的审美品质。作为我们实验的结果，我们通常可以推荐 L 型领导者作为衡量任务绩效和主观偏好评分之间的最佳折衷方案，而直人和斜线领导者在这两种衡量标准中获得的评分不一。从实用的角度来看，一般不推荐 S 形引线。