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High Resolution 3D Scanning of Paintings using a XYZ-RGB Portable Color Scanner at the C2RMF

2004 - Paris, France

As part of an ongoing research collaboration between the National Research Council of Canada (NRC) and the Centre de Recherche et de Restauration des Musées de France (C2RMF), a team of 3D imaging scientists from NRC’s Institute of Information Technology visited the C2RMF in Paris from May 10 to 19, 2004.

The objective was to scan a series of paintings to demonstrate the applications of high-resolution 3D imaging for documentation and conservation recording of paintings as well as to obtain 3D image data for ongoing research collaboration between NRC and the C2RMF.

For the project, NRC took two of its most advanced 3D imaging systems – the newly developed portable High-Resolution Color Laser Scanner as well as the Large Volume of View or “Big Scan” Laser Scanner – to Paris. During the visit, the team scanned four paintings – front and rear. The four paintings were an anonymous Spanish panel painting Dame en Prière and three oil on canvas paintings by Renoir, Femme Nue Dans un Paysage, Gabrielle et Jean and Portrait d’un Jeune Homme et d’une Jeune Fille.

The High-Resolution RGB Color Laser Scanner was used to acquire the very fine 3D and color details of the surface of paintings with a range resolution of 10 µm. The Big Scan second system designed for larger volumes had two main roles: to acquire the overall shape of the painting and to track and monitor the position of the high-resolution laser range scanner for global positioning.

A unique feature of 3D optical scanning for the examination of paintings with varnished surfaces is that the shape data recorded by the scanner originates from the surface of the paint layer, under the varnish, rather than from the varnish surface. This results in a detailed high-resolution recording of the surface relief or 3D structure of the paint layer from brush stroke details as well as craquelure formations due to ageing. No other technique (other than optical) captures this type of information. However the effects due to change of index of refraction of the varnish are still the subject of investigation; the real-surface of the painting will be closer depending on the angle of incidence of the laser light and of the thickness of the varnish layer. (For more information see Blais et al, 2005. Ultra-High Resolution Imaging at 50 µm using a Portable XYZ-RGB Color Laser Scanner, NRC 48099).

Figure 1: The 3D scanners used to scan Femme Nue Dans une Paysage at the C2RMF. The High-Resolution Color Laser Scanner (foreground) is mounted on a linear translation stage for scanning the painting. The Large Volume scanner mounted on a tripod (rear) is used to generate a scanning grid pattern (Figure 2) and to monitor in real-time the position of the High-Resolution scanner. Bottom-left Lissajous tracking pattern on the spheres mounted on the Color Laser Scanner.

Figure 2: The Large Volume Scanner tracking system monitors the position of the painting and automatically generates a grid pattern. Each grid accurately indicates the sections to be scanned to minimize overlapping areas. The tracking system also records the overall shape of the painting to a resolution of 200 micrometers.

Figure 3: Figure 3: 3D Color image (left) and Artificial Shaded monochrome image (right) of Femme Nue.

Figure 3: 3D Color image (left) and Artificial Shaded monochrome image (right) of Femme Nue. The artificial shaded image is similar to raking light photography and enables examination of brushstroke features and other surface details. The painting was scanned at a resolution of 50µm in the lateral x and y directions and 10µm in depth or the z direction. File Size is 150 Mega Pixels.
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Figure 4: Detail of face of Femme Nue . The Craquelure is visible in the color image (top). The shaded monochrome image of same area (bottom) shows the canvas relief due to thin paint layer.

Figure 5: Artificial Shaded image detail of Femme Nue illustrating brush stroke details.
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Figure 6: The color-coded shape image on the right records the distorted shape of the wooden panel of this circa 1775 – 1799 Spanish painting Dame en Priere. The color scale ranges from – 500µm red to + 500µm purple with bluish-green = 0. Color-coded shape images can be used to accurately document the shape of the panel as well as to monitor ongoing shape changes with time.
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