Paper Conservation: Decisions & Compromises

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ther because the user failed to focus the camera tightly enough, or because the camera was too far away from the subject (a possible restriction due to limited gutter opening space for bound collection items). Unsharp mask is a command in the ImageJ Process menu which subtracts a blurred duplicate of the image followed by a rescaling of the image to obtain the same contrast of large low-frequency structures as in the original. The image is sharpened as this process is equivalent to adding a high-pass filtered image to the input image. Unsharp mask is the final operation which should be applied to an image during processing. It is a destructive process. Images can also be sharpened using Process > Sharpen but the user has no parameter control (blur radius and strength of filtering). Unsharp mask changes colour values and is especially destructive in the fine gradations of colour which form part of the image that is most vital in enhancement processes. Smooth backgrounds become grainy and lose subtle colour definition crucial to restoration, while boundaries become more well-defined (Fig. 4). Conclusion A suite of processing and analysing features in the ImageJ package offers multiple applications to the field of cultural heritage including image file distribution, digital image enhancement, metadata generation, watermark extraction, colour management, provenance determination, degradation monitoring, artifact interpretation, scholarly understanding and publication, and boundary definition. The increase in digitisation projects generates large volumes of image files that can be processed to enhance understanding of our collections, without physically handling fragile material. References Barilla, M.E. of the Digital Systems & Vision Processing Group at The University of Birmingham, UK is the author of the ImageJ plugin ‘Color Transformer’. The first version was released in 2007 and was last updated in 2012. http://rsbweb.nih.gov/ij/plugins/color-transforms. html. Faigenbaum, S, Sober, B., Shaus, A., Moinester, M., Piasetzky, E., Bearman, G., Cordonsky, M., and Finkelstein, I., Multispectral images of ostraca: acquisition and analysis, Journal of Archaeological Science, Volume 39, Issue 12, December 2012, Pages 3581-3590. McFeely, C., An introduction to digital restoration techniques using high resolution digital images, The DIAMM Digital Restoration Workbook, 2006. Schwartzwald, D is the author of the ImageJ plugin ‘Color Space Converter’. The first version was released in 2006 and was last updated in 2007. Figure Captions Fig. 1: Brightness and Contrast. (a): original image, (b): brightness and contrast adjusted image. The image is processed using the automatic brightness and contrast command which optimises the settings based on the image’s histogram. (Image: Cotton MS Nero D.IV Folio 89v). Fig. 2: Merging and Splitting Channels. (a): multispectral image at 420 nm, (b) multispectral image at 720 nm, (c): multispectral image at 1,000 nm, (d): pseudocolour image which is the sum of (a), (b) and (c) where colours are assigned as (a) = red, (b) = green and (c) = blue. (Image: Add. Ms. 45722, Leaf from Sforza Hours). Fig. 3: Rotation and Transformation. (a): unrotated original image of the letter a, (b): rotated image of the letter a, (c): unrotated close-up of the letter a showing pixel distribution, (d): rotated close-up of the letter a showing increased pixel blur when compared to (c). (Image: Cotton Augustus ii 106). Fig. 4: Unsharp Mask: (a): original unsharpened image, (b): image after Unsharp Mask command is applied once, (c): unsharp mask command is applied twice, (d): unsharp mask is applied three times. (Image: Add. Ms. 45722, Leaf from Sforza Hours). Author Christina Duffy The British Library, 96 Euston Road, London, NW1 2DB, United Kingdom, christina.duffy@bl.uk. ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013 130
Analysing Deterioration Artifacts in Archival Material Using Multispectral Images Christina Duffy The British Library, London, UK Introduction Multispectral imaging is a non-invasive and nondestructive method with applications in remote sensing, astronomy and most recently in the emerging field of cultural heritage. Details of archival material invisible to the naked eye may be revealed by examining them in the infra-red (IR) and ultra-violet (UV) regions of the spectrum. Unlike standard RGB imaging, multispectral imaging captures a dense set of spectral measurements over a wide wavelength range revealing information unobserved in the visible bands. Deteriorating artifacts in archival material can be analysed and documented by processing digital images generated by multispectral instruments, without the risk of damaging the primary source. Archival degradation is present in all materials due to natural aging and can be accelerated by usage, poor storage conditions, unsuitable humidity, mould and insect infestations, and physical damage such as fires or floods. These conditions lead to typical deterioration artifacts including biological and physical damages, metal gall inks corrosion, ink diffusion and fading, seeping of ink from overleaf (bleed-through effect), blurred or unfocused writings, transparency, parchment gelatinisation, noise, spots, fragmentation of ink, or paper oxidation. Examining these artifacts in different regions of the spectrum enables differently-coloured features to be emphasised so that deterioration artifacts may be distinguished and damage may become visible. Multispectral Imaging: The range of all possible frequencies of electromagnetic (EM) radiation is known as the Electromagnetic Spectrum. It extends from low frequency and long-wave radio waves through to high frequency and short gamma waves. The higher the frequency, the more energy a wave contains. These energetic waves can cause serious damage to sensitive material, including skin when exposed to UV radiation from the sun. Radiation either side of the visible region cannot be observed with the human eye, but can be captured visually using multispectral analysis. Multispectral imaging is a form of computational photography which extracts information from a sequence of digital images. Computational photography is based on the interaction of light with matter. When light falls on an object, energy is absorbed, reflected or transmitted by its surface. The extent to which this energy is absorbed or reflected is dependent upon the chemical nature of the object. Each material will have a characteristic spectral curve dependent on the chemical make-up. Multispectral instruments can provide spatially-resolved analysis and distribution of materials with distinct spectral signatures. Many texts which are illegible to the eye are legible in the infrared. Similarly, deterioration artifacts that cannot be seen in the visible can be observed at other wavelengths. Fig. 1 Experimental Method Hardware: A number of multispectral imaging systems are available on the market, but each developed for a specific purpose. One of the first systems designed for cultural heritage was developed and used for high resolution digitisation of large easel paintings at the National Gallery under the EU-funded VASARI project (Saunders 1993). Since the VASARI project multiple systems ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013 131
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Paper Conservation: Decisions & Com
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Content Lieve Watteeuw Introduction
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Michael Wheeler | Nicholas Barnard
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New Trends in Preservation in the D
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and monitoring against adverse envi
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Steve Hobaica, Patrick Loughney, Ma
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The Albums of Duke Charles de Croÿ
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Fig. 4: turning the supporting pape
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Fig. 2: Close-up of some of the los
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manuscript paper, the binding would
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Figure 2 partial sewing: the blue d
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Books in Exhibitions: History and A
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Fig. 4 Museum in London and the pre
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Risk and Safety of Illuminated Manu
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Fig. 2 Atlas, the Crown papers are
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Acknowledgments The authors would l
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Verdigris I: Compromises in Conserv
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Verdigris 2: Wet Chemical Treatment
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Integrated Modelling: The Demograph
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Fig. 3: The consequence of 50 insta
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Characterisation of Historical Pape
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pling is required, tide-lines are c
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Study of Phytate Chelating Treatmen
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Evaluation of stochiometric effects
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Practice and Progress in the Conser
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Fig. 1 Fig. 2 plex picture and prov
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Fig. 2: Coloured paper strips place
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the fire (on the other hand paper,
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inform decisions on conservation tr
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This paper summarizes what is known
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2. Methods An interdisciplinary met
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Fig. 4: Dyed endpaper pasted at the
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Preservation of Architectural Drawi
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Notes 1 According Salvador Muñoz V
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course of time under the influence
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the curators in review of the treat
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cellulose powders with cellulose et
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Authors Xing Kung Liao Conservator
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Fig. 2: Our Railroad Workers and th
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Page 123 and 124: Fig. 2: Patriarchs of Chan Buddhism
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