FINGERPRINT in KU Leuven Campuskrant

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Cartoon by Joris Snaert © on the use of the Portable Light Dome when digitizing a Bruegel drawing (page 2 of Campuskrant 31/1) 

In an interview in the KU Leuven university journal Campuskrant with prof. Lieve Watteeuw the KU Leuven contributions to the FINGERPRINT project have been highlighted in length. The Campus article focuses on the work with the original drawings by Pieter Bruegel the Elder and how the imaging effort by the FINGERPRINT-team have made the difference to better understand the virtuosity of Breugel the artist.  These results will also be presented on the KBR exhibition: The World of Bruegel in Black and White.

PDF of the complete campuskrant edition

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Two page article on the Bruegel research by the KU Leuven in the FINGERPRINT project (©Campuskrant 31/1, pages 9-8) 


Scientific and Technical Imaging of the Bruegel Drawings

One of these unique moments, March 6-7 2018, location Royal Library Brussels (KBR): five drawings bearing a signature by Bruegel brought together to image them all with the same equipment, procedures and settings. Four drawings form part of the KBR collection of the Print Room and one is kept at the Royal Museums of Fine Arts of Belgium, likewise in Brussels.

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Details on standard metamorfoze photographs: The Bruegel / Brueghel signatures on the five drawings

In a previous blog post the toolbox of the applied imaging techniques within the FINGERPRINT project was already summed up. Since then, the applied band-pass filter set for the multispectral recordings was improved and expanded. A set of new filters (MidOpt), starting from 365nm in the UV and ranging over the visual spectrum up till 940nm in the IR, was selected. All together they assure a full coverage of the wide spectral reflective responses of the paper and applied inks of the drawings. The set consists of the following filters:

BP550 (VIS); BP324 (Near-UV & Near IR); Bi405 (Violet edge); Bi440 (Violet); BP505 (Cyan); BP590 (Orange); BP635 (Light red); BP660 (Dark red); BP695 (Red & Near IR); Bi725 (Red edge); Bi780  (Near IR); Bi830 (Near IR); Bi880 (Near IR); BN940 (Near IR).

For every drawing the recto and, when possible, the verso were recorded with all filters, i.e. each filter mounted separately on a full spectrum Nikon D610 while the drawings were exposed to the incident light of two studio flashlights (Elinchrom style RX600) or with the BP324 filter exposed to the light of a UV 365nm tube; 14 recordings per side in total. One extra capture was produced with UV radiation and the VIS filter mounted to obtain a UV florescence image. As intended with MS photography, the use of various spectral bands is able to reveal and accentuate other characteristics compared to standard visual / white light photography; as illustration the example below.

The Bruegel-signature in light brown ink on the Strait of Messina drawing (i.e. a drawing after Pieter Bruegel the Elder) is difficult to read and to distinguish from the paper background. When a number of the multispectral results are presented next to each other, the letters become better legible when only spectral bands with shorter wavelengths are used. Further processing of these images with techniques such as PCA could reveal other information.


Screenshot from comparison viewing mode in Capture One Pro 10.2.1 of detail on Strait of Messina – KBR F-2011-138: results of recordings with various MS filters, whether or not visualizing properly the Bruegel signature

A second example (just below) with the results of the MS photography can be observed on the Bruegel drawing from the Royal Museums of Fine Arts of Belgium: Prudentia. In certain cases spectral imaging allows you to reveal information on the drawing’s conservation history. Details and features otherwise difficult to distinguish can be monitored and visualized. Standard high resolution photographic documentation (i.e. VIS) barely visualises small, perfectly executed restorations of the paper. However, as the composition of the modern paper differs from the original historical paper, the UV Florescence of both similar but nevertheless different materials react with the incident light and emit this energy in their own easily to distinguish manner.


Screenshot from comparison viewing mode in Capture One Pro 10.2.1 of detail on Prudentia – KMSKB 4060-490: results of recordings with standard VIS photography (below) and UV Fluorescence

In addition to standard high resolution photography (Phase One IQ1) and the MS Filter photography (Nikon D610), all drawings were also imaged with the KU Leuven Portable Light Dome (PLD) system; both with the White Light (WL) and Multispectral (MS) modules. These reflectance images, based on the principles of photometric stereo, provide, pixel per pixel, interactive in-depth visualisations and the extraction of metric data on the material characteristics, i.e. their spectral behaviour and on the topography of the artefact.


Bruegel’s Stream with Angler – KBR SII113145 under the White Light Portable Light Dome (three WL LED emitters illuminated for demonstration purposes)


Bruegel’s Luxuria – KBR SII132816 under the Multispectral Portable Light Dome
(one of the green LED emitters illuminated and one shell removed for demonstration purposes)

Bruegel’s design on paper was transferred onto copper plates by the engraver through tracing the ink lines with a stylus. When the drawings are observed with the naked eye, or inspected by means of the standard high resolution Metamorfoze photographs (see below), these indentation lines can barely be distinguished on the surface. These lines are very shallow and remain largely obscured by the ink design. When raking light is introduced these indentations become more visible; therefore all drawings were photographed twice in a standardized manner, with light coming from the left side of the drawing and light coming from the bottom/below. Although the presence of the original design still makes it challenging to identify all the indentations made by the engraver on Bruegel’s drawing, some of them are clearly visible.

The interactive PLD renderings provide even better insight in the presence of these indentation lines. In the MS PLD dataset of the original drawing, the PLDviewer software can isolate and visualize all the tracing lines ­­by combining both the virtual relighting tool and the shaded filter. The first provides the necessary raking light, which drops shadows, illuminates edges and so makes the indentations contrast with the main flat surface. The latter omits the color of the surface, so Bruegel’s ink design. (In the example below the shaded MS PLD image has a underlying normal map based on the dataset with the Blue spectral responses)

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Screenshot from comparison viewing mode Cumulus Client 9.1.1 of detail on Bruegel’s Prudentia drawing (KMSKB 4060-490), images made with Phase One IQ1 and MS Portable Light Dome (i.e. microdome)

In the upcoming months these various types of images of the Bruegel drawings will provide art historians and conservators a solid set of data to empower there study, work strategies and aimed insights. The imaging of the these five drawings was made possible thanks to the joined efforts by the entire FINGERPRINT-team.

Introduction article

A first introduction article on the FINGERPRINT project has been published in the journal Science Connection by the Belgian Science Policy Agency Belpso:

Joris Van Grieken, Lieve Watteeuw, Bruno Vandermeulen, Marc Proesmans & Maarten Bassens 2017:

  • Fingerprint onderzoekt Pieter Bruegel de oude: De start van een interdisciplinaire studie van zijn tekeningen en prenten (Dutch version),
  • Fingerprint, projet de recherche sur Pieter Bruegel l’Ancien: Le lancement d’une étude interdisciplinair de ses dessins et estampes (French version),

in: Science Connection 45, 32-36.

La Kermesse de la Saint-Georges de Bruegel sous le Microdome

Looking closer to Materials and Methods of Transfer in “Justitia” of Pieter Breugel the Elder

picture6The Fingerprint art historians and conservators are looking close to identify and visualise the inks and indentation patterns in the drawings of Pieter Breugel the Elder. The drawing of “Justitia” ( Royal library S II 133 707) is in february 2017 in focus. Detailed material discription and imaging techniques are revealing new information on the creation of the drawing.


FINGERPRINT: the toolbox

FINGERPRINT involves the collection and processing of a large amount of visual and material data. To obtain that visual data we have an extensive toolbox at our disposal: a high resolution medium format digital back, a motorized repro stand, a Nikon DSLR modified for multispectral imaging with a collection of multispectral filters, the RICH microdomes and much more. A brief overview.

Cambo Actus with Phase One digital back and Schneider-Kreuznach lenses


To capture high resolution images we are using a Cambo Actus view camera with a Phase One IQ180 medium format digital back (to be upgraded to the IQ1 100 in the near future), a Schneider-Kreuznach apo-digitar 4.0/80 and a Schneider-Kreuznach apo-digitar 5.6/120. Both lenses are mounted in Schneider electronic leaf shutters which can be controlled through software and allow for very fine exposure adjustments (1/10th of a stop). Because the Cambo Actus does not have a mirror like DSLR cameras, there is no risk of unsharpness due to the vibrations of the actuating mirror. Combined with the Schneider leaf shutters, renowned for their lack of vibration, this enables us to capture extremely sharp images with lots of fine detail and nuance.


Cambo RPS repro stand

Because the Phase One backs have such a high pixel count, the camera support needs to be extremely stable. Even the slightest instability would have adverse effects on image quality. For FINGERPRINT, we are using a Cambo RPS repro stand. The RPS stand features geared electronic movements, allowing for precise and reproducible setting of the camera height.

Novoflex CASTEL XQ II quick release

To attach the camera to the Cambo RPS, a Novoflex Castel XQ II is used. This might seem to be an unspectacular item, but it is critical for securely fastening the camera to the RPS stand. Again, any chance of vibration is to be avoided. Moreover, the Novoflex allows us to move the camera equipment parallel to the baseboard of the repro stand, thereby enabling us to image different parts of an engraving or a drawing without the need to move the artefact underneath the camera.

Modified Nikon D610


The visual data that is used for FINGERPRINT will not be limited to the visible spectrum. A Nikon D610 with a modified sensor makes it possible to capture images in the UV and near-infrared spectra. These multispectral images are a great tool, for example to distinguish between different types of ink or to study underdrawings. To control which wavelengths are captured, we use a set of Edmund Optics OD 4 10 nm bandpass filters. These filters transmit a very narrow band of the spectrum of light (10 nanometres wide), allowing us to collect a very precise set of visual data.

And of course the RICH microdomes:

Introducing Fingerprint


Pieter Bruegel, Justitia, S II 133 707 (detail), 1559, 224 x 295 mm, KBR Print Room, Brussels, Imaging with Multi-Spectral Microdome (RICH)

FINGERPRINT is an interdisciplinary collection and data management project, involving art history, art technical research, digital imaging, image processing and conservation science. The aim is to use advanced digital imaging, statistical processing and laboratory analyses to monitor and evaluate the phases of the genesis of a print, from preparatory drawings through proof impressions to later states and editions. The four year project (2016-2020) is a collaboration of the Print Room of the Royal Library of Belgium and three KU Leuven teams: the Imaging Lab, ESAT and Illuminare, Centre for the Study of Medieval Art. The research project is funded by Belspo BRAIN-be (Belgian Research Action through Interdisciplinary Networks). The Royal Institute of Cultural Heritage (KIKIRPA), Brussels and the international research project on the materials and techniques of Pieter Bruegel the Elder (KHM, Vienna) are main research partners.

Up to now art historical research on prints and drawings has depended for the most part on traditional art historical methods based on observation with the naked eye and on the subjective memory and knowledge of connoisseurs. The aim of this project is to develop tools to automatically perform an objective artefact analysis and software to visualize, compare and order large quantities of complex visual and material data. Special processing algorithms will be developed to analyse visual data.

The exceptional collection of graphic works by Pieter Bruegel the Elder (ca. 1520-1569) in the Royal Library of Belgium forms a test corpus for the FINGERPRINT project. The tools and methods developed to gather and process the data will be designed to answer specific questions related not only to collection management, technical art history and conservation science but also to the production, distribution and consumption history of this body of works by Bruegel.

The datasets created on the multiple research platforms of FINGERPRINT and the resulting new interpretations will be accessible to both the scholarly community and the general public through links to the descriptions of the artifacts in the online public access database.