1. Documenting a 19th Century British Painting
Using Multispectral and Computational Imaging
A 19th century British landscape painting was documented using a combination of
portable digital technologies. Documentation of the recto consisted of Reflectance
Transformation Imaging (RTI), photogrammetry, and multispectral imaging (ultraviolet
reflectance and fluorescence, visible, and infrared reflectance). Documentation of
the verso consisted of photogrammetry and transmitted infrared (IR) imaging to look
for canvas-maker’s stamps and other features on the original canvas, which is glue-
lined, that could be correlated with a date when the canvas was supplied. Close-range
photogrammetry generated a calibrated three-dimensional (3D) surface model of the
recto and verso of the painting, allowing high-resolution multispectral image cubes to
be stitched into complete orthorectified images for each waveband.
Transmitted IR images of the verso revealed two canvas-maker’s stamps that were
partly obscured by the horizontal cross-brace of the stretcher. To allow more detailed
comparisons and measurements of the canvas stamps, registered visible and
transmitted IR images of the canvas were aligned with the 3D model. A transmitted
IR orthophoto of the verso was exported from the 3D model. Additional transmitted
IR images were captured with the camera positioned at an angle above and below
the stretcher’s cross-brace to capture more of the obscured text of the stamps. The
distortion-corrected images of the stamps were stitched together for archival purposes
and to allow detailed study and comparisons between the two stamps. The stamps
identified the name and location of the canvas supplier in London and established a
date range for when the original canvas was supplied (1834 to ca. 1860).
ABSTRACT
Intern, Digital Diagnostic Specialist, Kept Art Restoration
President, MegaVision, Inc.
Principal Scientist, Equipoise Imaging, LLC
Taylor Bennett
Ken Boydston
William Christens-Barry
RECTO VERSO
Figure 1. Giudecca Canal and Santa Maria della Salute, Venice (92 cm x 127 cm or 36 inches x 50 inches).
Color image reconstructed from six visible wavebands at 455 nm, 470 nm, 505 nm, 535 nm, 570 nm, and
625 nm.
Figure 2. The painting has been glue-lined, obscuring the original canvas and canvas maker’s stamps.
An augmented reality (AR) application allows interactive overlay of transmitted infrared images
(Figures 8-9) on mobile devices, displaying the positions of canvas maker’s stamps.
Figure 4: Photogrammetry extracts shape information from multiple overlapping images (camera positions
represented by blue rectangles) to generate 3D models of the recto (a) and verso (b) of the painting. Calibrated
3D models were used to export orthorectified images, stitch images of multispectral wavebands, and align
transmitted infrared images.
Figure 3. Reflectance Transformation Imaging (RTI) combines multiple images to extract a detailed map of
surface texture. This detail of the painting shows default normal (a) and interactive (b) relighting and application
of specular enhancement, one of several algorithms available in the RTIViewer. Specular enhancement with
relighting reveals the texture of impasto, craquelure, and brushstrokes.
PHOTOGRAMMETRY
Figure 8. Transmitted infrared orthphoto of verso, showing locations of two canvas maker’s stamps partly ob-
scured by the cross-brace of the stretcher. Additional transmitted infrared images were captured at an angle
from above and below the cross-brace, allowing reconstruction of the canvas stamps shown in Figure 9.
Wavelength, λ (nm)
625 nm
(VIS-Red)455 nm
(VIS-Violet)
470 nm
(VIS-Blue)
505 nm
(VIS-Cyan)
535 nm
(VIS-Green)
570 nm
(VIS-Amber)
LED Spectra
λ
700 nm
(IR)
735 nm
(IR)
780 nm
(IR)
870 nm
(IR)
940 nm
(IR)
365 nm
(UV)
RECONSTRUCTION OF CANVAS MAKER’S STAMPS
Figure 9. Details of canvas stamps A (a) and B (b) identified in Figure 8. The two stamps were reconstructed
from transmitted IR images captured at an angle from above and below the horizontal cross-brace of the
stretcher, aligned with the transmitted IR orthophoto exported from the 3D model, and stitched together.
The text of the stamps is interpreted as “HOLT/ ARTISTS’ COLOURMAN/ 80 GOSWELL ROAD/ Opposite
[illegible]/ ISLINGTON.” Available records indicate John Holt (b. 1802-1874) was initially active as an oil and
colourman and artists’colourman at 31 East St. (now called Chiltern St.), Marylebone, and later at 80 Goswell
Road, Islington, from 1834 to ca. 1860 (T. Bennett, 2015).
Figure 5. Emission spectra of light emitting diodes (LEDs) used
for multispectral reflectance imaging. Two panels consisting of
12 LEDs were used: one ultraviolet (UV), six visible, and five
infrared (IR).
Figure 6. One of 16 image cubes consisting of 12 wave-
bands captured using a MegaVision camera with a 50
megapixel monochrome CCD sensor and apochromatic
lens.
a
Reference:
Bennett, T. (2015). Photogrammetry and Transmitted Infrared Imaging to Document the Support of a 19th C. British Landscape Painting.
Manuscript accepted for publication in the e-bulletin of Color and Space in Cultural Heritage (COSCH).
ACKNOWLEDGEMENTS
Cultural Heritage Imaging (CHI), a 501(c)3 non-profit (culturalheritageimaging.org)
James Wright, Conservator, Somerville, Massachusetts, USA
Kept Art Restoration (www.keptartrestoration.com)
Giovanni Landi, Mixed Reality Architect, Piazza Santa Brigida 15/16a, 16123, Genova, Italy
REFLECTANCE TRANSFORMATION IMAGING (RTI)
MULTISPECTRAL IMAGING TRANSMITTED INFRARED IMAGING
b
a
a b
b
a. UV Reflectance (365 nm) b. UV-Induced Visible Fluorescence c. Infrared Reflectance (940 nm)
Figure 7.
FUTURE WORK
a. UV reflectance (365 nm). Dark patches in sky indicate retouching, possibly with titanium white, a pigment
introduced in the 1920s.
b. UV-induced visible fluorescence using 365 nm excitation wavelength and a UV blocking filter on the lens to
block reflected UV. Visible fluorescence image is reconstructed from three wavebands using red, green, and
blue bandpass filters on the lens (Wratten #25, #58, and #47 filters, respectively).
c. Infraredreflectance(940nm),oneofthefiveinfraredreflectancewavebands(theotherfourinfraredwavebands
are centered at 700, 735, 780, and 870 nm).
Future work to understand the history and materials of this painting is anticipated to include the following:
• Pigment mapping to further define areas of retouching and to aid in selecting locations for possible non-invasive analysis,
such as x-ray fluorescence spectroscopy (XRF), Raman spectroscopy, and fiber-optic reflectance spectroscopy (FORS)
• Pigment sampling and analysis of cross-sections to assess the results of non-invasive techniques
• Comparison of the palette with similar paintings by known artists
• Further research into the history of the artists’ colourman, John Holt, who supplied the original canvas for the painting