Headwall’s SWIR 640 sensor is part of world-famous Operation Night Watch by the Rijksmuseum, and is mentioned in the first published work in Sensors 2021, 21(20), 6855, Reflectance Imaging Spectroscopy (RIS) for Operation Night Watch: Challenges and Achievements of Imaging Rembrandt’s Masterpiece in the Glass Chamber at the Rijksmuseum by Francesca Gabrieli 1,*, John K. Delaney 2, Robert G. Erdmann 1,3, Victor Gonzalez 1, Annelies van Loon 1,4, Patrick Smulders 5, Roy Berkeveld 5, Robert van Langh 1, and Katrien Keune 1,6
Headwall-created animated GIF (featured image). Caption from Figure 3 from the paper: Accurate color image calculated from the VNIR reflectance imaging dataset using D65 standard illumination and a false color image of the SWIR image cube prepared using 1603 nm, 1201 nm and 1040 nm spectral bands for the RGB channels.
Abstract
Visible and infrared reflectance imaging spectroscopy is one of the several non-invasive techniques used during Operation Night Watch for the study of Rembrandt’s iconic masterpiece The Night Watch (1642). The goals of this project include the identification and mapping of the artists’ materials, providing information about the painting technique used as well as documenting the painting’s current state and ultimately determining the possible conservation plan. The large size of the painting (3.78mby 4.53 m) and the diversity of the technical investigations being performed make Operation Night Watch the largest research project ever undertaken at the Rijksmuseum. To construct a complete reflectance image cube at a high spatial resolution (168 m2) and spectral resolution (2.54 to 6 nm), the painting was imaged with two high-sensitivity line scanning hyperspectral cameras (VNIR 400 to 1000 nm, 2.54 nm, and SWIR 900 to 2500 nm, 6 nm). Given the large size of the painting, a custom computer-controlled 3-D imaging frame was constructed to move each camera, along with lights, across the painting surface. A third axis, normal to the painting, was added along with a distance-sensing system which kept the cameras in focus during the scanning. A total of 200 hyperspectral image swaths were collected, mosaicked and registered to a high-resolution color image to sub-pixel accuracy using a novel registration algorithm. The preliminary analysis of the VNIR and SWIR reflectance images has identified many of the pigments used and their distribution across the painting. The SWIR, in particular, has provided an improved visualization of the preparatory sketches and changes in the painted composition. These data sets, when combined with the results from the other spectral imaging modalities and paint sample analyses, will provide the most complete understanding of the materials and painting techniques used by Rembrandt in The Night Watch.
