Tag Archives: Multispectral

Techniques for recovering lost texts

Research Fellow Renate Smithuis and Research Associate Stefania Silvestri, are working on a Catalogue of Codices, Scrolls, and Other Texts in Hebrew Script in The University of Manchester Library.

The Library holds one of the most important smaller collections of Hebrew manuscripts in Europe and this project will create a full, online catalogue compliant with current cataloguing and metadata standards. To support the production of the catalogue, digitisation of a number of manuscripts is being undertaken. All images, included fully digitised volumes, are added to the Hebraica Collection in the John Rylands Library Image Collections, LUNA.

A substantial portion of the Rylands Gaster manuscript collection have already been selected for digitisation, including a number of manuscripts that suffered water damage during the Second World War. The level of water damage varies, some texts are still legible but faint, others have whole sections of pages rendered illegible.

The Heritage Imaging Team have been investigating the best way to recover the text in these volumes, unsurprisingly, we have found that a single solution does not fit all. The aim of this blog post is to demonstrate the different processing options available to researchers. We are researcher-led in the work that we do with Multispectral Imaging of our collections, so if you come across a text you cannot read, please get in touch to discuss your needs in more detail (email: uml.chicc@manchester.ac.uk).

I should note at this point that these examples are not exhaustive and we are always in the process of developing new techniques.

Trials in image processing have been run on pages from Gaster Hebrew MS 1832. The first step of carrying out any specialist techniques is to produce a high resolution ‘standard’ light photographs. These are the images that you can access in high resolution in our online image collections. Often, close inspection at high resolution enables a reader to decipher more than they can read with the ‘naked eye’.

In this example, the first image shows page 1 recto of Gaster Hebrew MS 1832 in ‘standard’ light. You are able to see that there is some faded text on the page but it is extremely faded in some areas:

Gaster Hebrew MS 1832

Gaster Hebrew MS 1832 1 recto standard image

The second image shows a standard high resolution image which has undergone additional image processing in Photoshop. The image has been inverted to help the text show through in certain areas of the page.

Gaster Hebrew MS 1832

Gaster Hebrew MS 1832 1 recto standard image with processing

The third image shows page 1 recto again, a standard high resolution image which has undergone processing in Photoshop to bring out the most faded central areas of the text.

Gaster Hebrew MS 1832

Gaster Hebrew MS 1832 1 recto standard image with additional processing

Here is a detail from each file type for comparison:

The benefit of this approach is that these results can be achieved without any additional imaging of the manuscript and standard photo manipulation software can be used. In addition, once results have been achieved, these can be batch applied to a set of images for an entire manuscript. The results may not be 100% consistent depending upon the range of damage to each page, but if the results are ‘good enough’ it will save many hours of image processing time.

 

Our next example shows firstly, page 2 recto of Gaster Hebrew MS 1832 in ‘standard’ light, plus an example of the same image which has been processed in Photoshop:

However, with this example we took several further steps to recover the lost text. In this instance, the manuscript has also been imaged using Multispectral Imaging. We now use a Phase One Achromatic IQ260 digital back, iXr camera body and standard lens combined with Megavision LED lighting panels and a filter wheel to capture 17 images at different points along the electromagnetic spectrum. I have included 2 images here, take at 370nm (UV) with a long pass violet filter, and at 448nm (Deep blue) as these single images give the best results. In the infrared wavelength, the text on this manuscript disappeared completely, which suggests that it is an iron gall based ink.

 

Using multispectral imaging we are able to take our image processing and textual recovery even further. Using ImageJ software I have combined several of the individual wavelengths to create a ‘pseudocolour’ image. This applies false colours to areas of difference across the page. Note the two images below in colour.

The colour results are not attractive to every eye, especially to the colour blind so can be converted in to greyscale. In the examples here, I have added an additional filter using the Channel Mixer in Photoshop to increase the contrast of the text even further.

Here you can see details of all 8 examples described above, click on the image to flick through each detail.

There are obvious benefits of taking every possible step of image processing to recover as much text as possible. However, there are also drawbacks. The manuscript must be subjected to a second round of digitisation using the Multispectral Imaging system, this is not only time consuming, but for fragile items it also increases the possible risk of damage to the physical item. There is additional time required for the photographer to process the images and store the additional data. Metadata must be produced to accompany the new images and to detail the processing work that has been carried out on the images.

Finally depending upon the nature of the damage to the page, a reader may need to consult a combination of 2 or 3 final processed images in order to read the entire page. Additionally, there must be a flow of communication between the reader/researcher and the person processing the images in order to process the ‘best’ results.

Specialists are currently working on software solutions to allow us to present the data to readers which will allow the reader themselves to combine and ‘play’ with images to suit their needs. We will report on developments in this area when they are available. Until then, we will continue to take a ‘triage’ approach to image recovery, assessing each item against the needs of the researcher to take the right steps to uncover lost texts.

 

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Multispectral Imaging Trials with The Photon Science Institute – George Christian and Robert Longstaff

 

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Measuring the wavelengths of the Megavision Panels using a spectrometer

 

We are all used to the fact that unique or very rare manuscripts, like those stored in the collections of the John Rylands Library, must be handled with extreme care. They are often only displayed to the public through a layer of protective glass or maybe even exclusively as photographic reproductions; the originals far too fragile to be brought out of the dark for extended periods of time.

Since they provide us with such a precious link to the past, it is very understandable that they should be treated in this way. So it might be easy to forget that this has not always been the case. There are many examples of manuscripts whose raw materials (usually parchment) were at one time deemed more valuable than the text they contained, and which therefore became palimpsests.

A palimpsest is a manuscript from which the text has been removed and replaced by new writing, effectively recycling the original material. This then creates a new challenge for scholars who wish to read the original text which may only be very faintly visible, if at all. Traditionally, the underlying text would have been read simply by close inspection of the faint impressions left by the writing. However, this is obviously limited to manuscripts for which this text is visible to the naked eye in the first place.

In the nineteenth and early twentieth centuries, scholars brought out the less visible text with various chemical cocktails which were often highly damaging to the manuscripts. More recently, far less invasive techniques have been developed based on a fundamental understanding of light and how it interacts with matter, and CHICC has teamed up with the Photon Science Institute (part of the School of Physics and Astronomy at the University of Manchester) to trial the technique of Multispectral Imaging.

We (George Christian and Robert Longstaff) are two fourth-year physics undergraduate students who are working with the imaging team to explore the potential usefulness of this technique. Multispectral imaging is the technique of capturing data (in this case photographs) from one source at multiple wavelengths of light. By treating these images as mathematical objects (where each pixel has a numerical value associated with it), they can be combined and manipulated in such ways as to produce images where the previously invisible text can be seen and interpreted (hopefully) much more easily. For example, often invisible text can be made very clearly visible by illuminating it with ultraviolet (UV) light. The trouble is, the text that replaced it is usually also just as visible in the image.

However, if an image taken at a wavelength where only the overlying text is visible is subtracted from the image where both texts are visible, then we are left with an image containing only the text that was previously very difficult or impossible to make out. The techniques we are using were employed on the now famous Archimedes Palimpsest, and the results they have achieved can be seen in full on their website (http://www.archimedespalimpsest.org/).

We have already had some success, although really we are learning as we go. Our main challenge is to find ways to bring out the “hidden” text as clearly as possible, and hopefully in a way that is useful to the scholars! This is a very exciting opportunity for us as it’s the first time this has been offered as a final-year project, and it offers a unique chance to work in the John Rylands Library which doesn’t happen very often for physics students!

George & Robert

George and Robert’s findings can be read here

 

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Spectral Imaging testing at The National Library of Scotland

Combe MS 7382 page 6 in visible light (left) and in UV light (right)

Combe MS 7382 page 6 in visible light (left) and at 365nm UV light with image inverted (right)

On 2nd July the CHICC photographers travelled to Edinburgh for some Multispectral Imaging testing on some George Combe letterbooks at the National Library of Scotland. Francine Millard of the NLS writes:

George Combe (1788-1858) was an Edinburgh lawyer who was among the first converts to phrenology. This was a science which believed that people’s characters could be read from the bumps in their skulls.

The National Library of Scotland holds a remarkable collection of George Combe’s papers from 1804 to 1872. The collection begins with his apprenticeship as a clerk to Writers to the Signet and charts his promotion of phrenology which included co-founding the Edinburgh Phrenological Society in 1820 and the works Elements of Phrenology (1824) and The Constitution of Man (1828). Combe’s outgoing and incoming correspondence document his efforts to spread the causes of phrenology, secular education, and criminal and prison reform.

 

Combe’s letterbooks contain a large proportion of his replies to his brother, Andrew Combe, who was also a fervent supporter of phrenology, and to those seeking his help and advice both in Britain and America. Combe’s replies were copied by wet letter press copying (or wet-transfer) and some pages in these books have now faded to the point of invisibility.

 

The National Library of Scotland teamed up with CHICC in July to see if multi-spectral imaging would be able to render Combe’s words visible. These tests would inform the Library on what approach to take to preserve the Combe papers through digitisation.

To find out more, watch this short film of the work in action:

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