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Contrast in Terahertz Images of Archival Documents-Part II: Influence of Topographic Features

Bardon, T; May, RK; Taday, PF; Strlic, M; (2017) Contrast in Terahertz Images of Archival Documents-Part II: Influence of Topographic Features. JOURNAL OF INFRARED MILLIMETER AND TERAHERTZ WAVES , 38 (4) pp. 467-482. 10.1007/s10762-016-0352-z. Green open access

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Abstract

We investigate the potential of terahertz time-domain imaging in reflection mode to reveal archival information in documents in a non-invasive way. In particular, this study explores the parameters and signal processing tools that can be used to produce well-contrasted terahertz images of topographic features commonly found in archival documents, such as indentations left by a writing tool, as well as sieve lines. While the amplitude of the waveforms at a specific time delay can provide the most contrasted and legible images of topographic features on flat paper or parchment sheets, this parameter may not be suitable for documents that have a highly irregular surface, such as water- or fire-damaged documents. For analysis of such documents, cross-correlation of the time-domain signals can instead yield images with good contrast. Analysis of the frequency-domain representation of terahertz waveforms can also provide well-contrasted images of topographic features, with improved spatial resolution when utilising high-frequency content. Finally, we point out some of the limitations of these means of analysis for extracting information relating to topographic features of interest from documents.

Type: Article
Title: Contrast in Terahertz Images of Archival Documents-Part II: Influence of Topographic Features
Open access status: An open access version is available from UCL Discovery
DOI: 10.1007/s10762-016-0352-z
Publisher version: http://dx.doi.org/10.1007/s10762-016-0352-z
Additional information: © The Author(s) 2017. Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Keywords: Science & Technology, Technology, Physical Sciences, Engineering, Electrical & Electronic, Optics, Physics, Applied, Engineering, Physics, Terahertz, Time domain, Imaging, Documents, Topography
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of the Built Environment
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of the Built Environment > Bartlett School Env, Energy and Resources
URI: https://discovery.ucl.ac.uk/id/eprint/1541342
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