Wunsch Conservation Laboratory, Massachusetts Institute of Technology (MIT) Libraries, Cambridge, MA, USA.
Adobe Research, San Francisco, CA, USA.
Nat Commun. 2021 Mar 2;12(1):1184. doi: 10.1038/s41467-021-21326-w.
Computational flattening algorithms have been successfully applied to X-ray microtomography scans of damaged historical documents, but have so far been limited to scrolls, books, and documents with one or two folds. The challenge tackled here is to reconstruct the intricate folds, tucks, and slits of unopened letters secured shut with "letterlocking," a practice-systematized in this paper-which underpinned global communications security for centuries before modern envelopes. We present a fully automatic computational approach for reconstructing and virtually unfolding volumetric scans of a locked letter with complex internal folding, producing legible images of the letter's contents and crease pattern while preserving letterlocking evidence. We demonstrate our method on four letterpackets from Renaissance Europe, reading the contents of one unopened letter for the first time. Using the results of virtual unfolding, we situate our findings within a novel letterlocking categorization chart based on our study of 250,000 historical letters.
计算扁平化算法已成功应用于受损历史文献的 X 射线断层扫描，但迄今为止仅限于卷轴、书籍和一到两折的文件。这里要解决的挑战是重建未打开的信件的复杂折痕、内折和狭缝，这些信件采用了“letterlocking”的方法，这一方法在信封出现之前的几个世纪里一直是全球通信安全的基础。我们提出了一种全自动的计算方法，用于重建和虚拟展开带有复杂内部折叠的锁定信件的体积扫描，在保留 letterlocking 证据的同时，生成信件内容和折痕模式的可读图像。我们在四个来自文艺复兴时期欧洲的信封装中展示了我们的方法，首次读取了一封未打开信件的内容。使用虚拟展开的结果，我们根据对 25 万封历史信件的研究，将我们的发现置于一个新的 letterlocking 分类图表中。
