DIAMM

Digital Image Archive of Medieval Music

Imaging

DIAMM has specialised in the digitization of rare and/or delicate documents, either bound or unbound. Our original remit was to digitize fragments of medieval music, and has extended to embrace complete manuscripts which are usually in better condition, but which present their own handling and conservation problems. Our photographers have long experience in handling delicate manuscripts and objects during their doctoral work, and since that time in handling manuscripts during photography.

Imaging priorities concentrate on obtaining the best possible picture without harm to the source, or stress to its binding. DIAMM does not use flash, and only uses ‘remote’ lighting (at a distance of over 1 metre) which does not generate heat, and is carefully engineered to exclude ultra-violet content, while emulating the colour spectrum of daylight (it is therefore less harmful than daylight). Our intention is that once imaging of a document has been completed by DIAMM, it should not be necessary to repeat digitization work again, thus digitization – as long as it is done to appropriate quality standards – fulfils a conservation purpose.

DIAMM does not have a studio, but normally works on site with the documents and their owners. In exceptional cases costs can be minimized by bringing the document(s) to Oxford for imaging work. We reserve the right to refuse to handle documents in order to obtain a particular image, in a way that we consider may shorten the life of the document, or damage it in any way.

There are two imaging processes available, and deciding which one is suitable for your source will depend on evaluation of your intended use of the images, and the size and condition of the source.

PhaseOne PowerPhase FX

Because of the cost of single-shot digital sensors, the highest-quality of digital imaging (i.e. obtaining the greatest number of pixels over the largest area) is done by using a scanning back. This has a double row of sensors, and the equipment acquires an image by taking multiple rows of pictures, in the same way as a flatbed scanner works. A single picture may take as long as 5-6 minutes to acquire.

However, a major difference between a scanning back and a flatbed scanner is that a scanning back is mounted on the back of a custom-built large-format camera body, and never touches the manuscript, nor does it have a bright light which is shone directly on the manuscript.

This equipment is able to yield images of approximately 132 megapixels (for comparison, high-end consumer cameras now capture at around 8-11 megapixels), and is most appropriate for:

  • Larger documents (A3 size and upwards);
  • Documents of any size that are damaged and for which imaging is intended to provide a surrogate for digital restoration;
  • Documents for which exceptionally high resolution is required for the end purpose.

The usual shot-rate for this camera is approx 80 shots per day, or up to 12 shots per hour. This is based on normal working hours and reasonable handling and access to the document. If a document requires more complex handling between shots the shot-rate will be lower. Please ensure that you have evaluated the document appropriately before attempting to calculate a shot-rate yourself. The photographer is available to make an initial visit to evaluate a document, or set of documents, for photographic work at a reduced daily consultancy rate.

Imaging is undertaken on a daily rate basis (plus travel and subsistence).

PhaseOne P45+

This is the first in a new generation of high-end single-shot cameras. Similar digital backs have been produced by Leaf, Hasselblad and Sinar, but most end users consider the quality of images from the PhaseOne P45+ to be superior. A very useful review may be found here.

A ‘single-shot camera’ means that the whole image is acquired in one action, so the camera works much as a normal digital SLR would do. The difference is in the size of the images. A high-end consumer digital SLR will capture images at 8-11 megapixels. The P45+ is able to capture images at 39 megapixels, thus yielding archive quality images for documents almost as large as A3 size, and quality well above this minimum for smaller documents.

    The P45+ is ideal for:

  • Small documents up to A4 size, or up to A3 if the source material is undamaged and the needs of the end-use do require a higher resolution
  • Projects where a large number of images are required in a short space of time, and where the source documents are in good condition.

The shot-rates for the P45+ have not been fully tested: because of the way the software works, capture time is relatively short, but we have to allow at least a day following the capture time for post-processing to produce the final images. We would expect to be able to obtain upwards of 600 images in a full day of shooting, or approx 100 images per hour. This estimate is based on easy document handling. If a document requires more complex handling between shots the shot-rate will be lower. Please ensure that you have evaluated the document appropriately before attempting to calculate a shot-rate yourself. The photographer is available to make an initial visit to evaluate a document, or set of documents, for photographic work at a reduced daily consultancy rate.

Imaging is undertaken on a daily rate basis (plus travel and subsistence).

A note on costs: we have compared our consultancy rates with charges made by the British Library and the Bodleian Library for images of the same quality, taken using the same equipment. Based on a two-day, full-time shoot in a library in Switzerland (i.e. including travel from the UK and subsistence expenses), resulting in 200 images in total, projects can usually obtain their images for approx. a tenth of the price of buying the same number of images from either of these institutions. This estimate is based on the use of the PowerPhase FX. Work done using the P45+ works out at less than one fiftieth of the cost of buying images from these suppliers.

Specialised and experimental imaging requirements

As long as there are no conservation problems with the source materials, we are happy to undertake experimental imaging processes in consultation with the researcher, including:

– Close-up shots;
– Raking normal (RGB) light, raking UV light;
– Transmissive light using a cold fibre-optic light sheet, ideal for documents which are stuck together, for faded ink, or for photographing watermarks;
– UV imaging using low-frequency ultra-violet lighting heads;
– Multi-spectral imaging using limited-bandwidth interference filters, which is particularly useful in dealing with very damaged (e.g. burned) documents and erasures;
– Infra-red imaging (limited effectiveness in the digital medium due to the very long exposure, which gives rise to ‘noise’ on the image).

UV photography uses low-frequency ‘blacklight’ ultra-violet lighting heads, which do not project the harmful UV that requires protective eye-wear and causes burns to the skin. Because of the low lighting levels, exposures are very long (up to 15 minutes using the FX scanning back, but depends on the size of the source and degree of fluorescence of the subject material under the UV light). Multi-spectral work is done using the P45+, and taking shots with a wide range exposures within the visible spectrum for each of eight filters: thus a set of multi-spectral images for a single leaf would comprise about 60 shots and take about 10-15 minutes to obtain after the document has been positioned. Transmissive light has proved successful in allowing material to be read from pages pasted together, and in photographing watermarks. The light sheet is thin enough to be inserted between pages in a book.

The success of these techniques, either singly or in combination, in obtaining data from damaged materials cannot be assured, as each source is different and results vary widely. However, we have found so far that the images always provide some additional information, even if it is not very much, and having tried these processes is a way of ensuring that all efforts have been made to read the document that are possible with current technology.

If you would like to enquire further about your requirements, or about a project that you are planning, please contact the Project Manager, Julia Craig-McFeely.