PolyWorks and the Mona Lisa - Innovmetric Software

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C A S E S T U D Y NRC scientists help solve the mysteries behind the Mona Lisa At the request of the Paintings Department of the Louvre, the Centre de recherche et de restauration des musées de France (C2RMF) undertook a study of the Mona Lisa. This study coincided with the relocalization of the painting to the new “Salle des États”, and is considered the most extensive scientific examination of a painting ever undertaken. As part of this project, the C2RMF invited a team of scientists from the NRC to participate, because of their renowned expertise in 3D imaging and modeling technologies. The NRC's role was to scan the complete painting - obverse and reverse - in order to prepare a complete high-resolution archival quality 3D model of the painting. The 3D model was required to: • Document and precisely measure the distorted shape of the poplar panel. • Examine surface features of the composition, the craquelure in the paint layer, the split in the panel, and the surface lacunae. • Discover visual caracteristics not visible to the naked eye that could lead historians to confirm theories and questions on the historical context of the painting. © National Research Council Canada 2
C A S E S T U D Y © National Research Council Canada Scan alignment in IMAlign module. Scanning the Mona Lisa with the NRC-IIT 3D scanner. Digitizing The study of the Mona Lisa was undertaken during the autumn of 2004. The NRC-IIT team had access to scan the painting for only a few hours over two evenings in October 2004. For the project, a high-resolution 3D color laser scanner, designed and built by the NRC-IIT, was brought to Paris to scan the painting. The triangulation-based system scanned a low-power white-laser spot over the painting in order to produce a high-resolution, archival-quality 3D digital model of the shape and color of the painting's surface. The data collected in 16 hours of 3D scanning (in 4-centimeter wide scans) required more than a year's worth of analysis. With a lateral resolution of 60 µm x 60 µm (0.06 mm x 0.06 mm), and at a depth resolution of 10 µm (0.01 mm), the NRC-IIT scanner was able to provide the most detailed analysis to date of the paintings’ network of surface cracks. Scan alignment The 3D color laser scanner was connected to the PolyWorks‚ software suite, the leading point-cloud-processing software developed by the Canadian firm InnovMetric Software Inc. A single pass of the scanner captured over 2,72M data points describing the shape (x,y,z) and the colour (R,G,B) of the painting. Seventy-two scans were taken from the front, thirty-two from the sides, and thirty-six from the rear to create a complete high-resolution 3D digital model of the painting. Each scan was automatically loaded in PolyWorks software on a real-time basis and aligned to neighboring scans, much like a giant puzzle. The alignment process was also done in real-time in the PolyWorks/IMAlign module using overlapping areas of the scans. François Blais Principal Research Officer and Technical Lead NRC-IIT “Having a live 3D rendering of what we were scanning was a crucial part of the digitizing process. This allowed us to evaluate immediately the quality of the scans and gave us the opportunity to rescan areas we missed as well as those that were of poor quality. We needed this information instantly, because there was no other chance for us to return and rescan the painting once our time had elapsed.” © National Research Council Canada 3
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PolyWorks and the Mona Lisa - Innovmetric Software

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