Virtual online museum
This is a worthwhile effort because, as Dr. Theobald Fuchs, chief scientist at Fraunhofer EZRT and MUSICES project leader explains: “A large part of the collections of musical instruments held by museums is kept in underground storage facilities. In case of the GNM there simply is not enough exhibition space to showcase all 3500 of them at the same time. The CT digitalization project will enable us to create a virtual museum in which digital facsimiles of these instruments are available to anyone with internet access.”
The team has already digitalized more than a hundred instruments dating back over several centuries – from the baroque trumpet and the mouth harmonica to the square piano. Different types of CT systems are needed to scan different-sized instruments. The square piano, for example, is X-rayed utilizing a linear accelerator, which is the source of radiation in Europe’s largest CT machine. The XXL X-ray environment consists of two eight-meter-tall steel scaffolding towers and a turntable with a diameter of three meters, housed in a hall covering a surface area of 400 square meters and rising to a height of 14 meters. Smaller string and wind instruments are X-rayed using conventional apparatus. For each test, the object is placed on a turntable between the X-ray source and typically a flat-panel detector, which produces images of very high spatial resolution. A specially designed holder keeps the instrument firmly in place while the X-ray beam penetrates the rotating object. The required dose of radiation varies according to the thickness and density of the material. Depending on the structure and condition of the instrument, the scanning process can take several hours, during which the CT system records several thousand images which are then stitched together to produce a three-dimensional view.
The researchers aim to publish their results online by January 2018 at the latest. These will not only include the collected CT data but also detailed and comprehensible documentation of all steps in the measurement process. The examination standard defines the CT scanning parameters, and the accompanying set of guidelines provides advice on its application for different instruments.
Openly accessible metadata
Moreover, at the end of the project, all the technical parameters and metadata will be published in a database developed at the GNM. “Ideally, we would like to be able to digitalize the museum’s entire collection of historical musical instruments and place the 3D images online. Our examination standard defines the best way to go about this task,” says Fuchs. “One of the many factors that we are now able to quantify is the time needed to digitalize different instruments. For example, a complete X-ray scan of a violin at a resolution of less than 50 microns takes up to 20 hours. This figure can be extrapolated to determine the time needed to scan an amount of x instruments. This produces a specific quantity of voluminous datasets, requiring corresponding amounts of hard disk and network capacity and special software. We have compiled a list of all these requirements.” Another advantage of the standard is that it enables the know-
ledge and experience gained from scanning musical instruments to be applied to other museum collections such as telescopes and other scientific instruments or old weapons.
Visitors to the “Long Night of Sciences” event in Fürth on October 21 will have the opportunity to take a look inside numerous historical musical instruments. One of the exhibitions will include a presentation of CT images by Fraunhofer EZRT, selected from among those produced during the project.