This paper presents a fully automatic computational approach for reconstructing and virtually unfolding volumetric scans of locked letters with complex internal folding, producing legible images of the letter’s contents and crease pattern while preserving letterlocking evidence. The method is demonstrated on four letterpackets from Renaissance Europe, successfully reading the contents of one unopened letter for the first time. The findings are situated within a novel letterlocking categorization chart based on a study of 250,000 historical letters.

Jana Dambrogio, Amanda Ghassaei, Daniel Starza Smith, Holly Jackson, Martin L. Demaine, Graham Davis, David Mills, Rebekah Ahrendt, Nadine Akkerman, David van der Linden, Erik D. Demaine