Panoramic, Macro and Micro Multispectral Imaging: An Affordable

Cosentino, A 2015 Panoramic, Macro and Micro Multispectral Imaging: An Affordable
System for Mapping Pigments on Artworks. Journal of Conservation and Museum
Studies, 13(1): 6, pp. 1–17, DOI: http://dx.doi.org/10.5334/jcms.1021224
RESEARCH ARTICLE
Panoramic, Macro and Micro Multispectral Imaging: An
Affordable System for Mapping Pigments on Artworks
Antonino Cosentino*
Multispectral imaging systems are used in art examinations to map and identify pigments, binders and
areas of retouching. A monochromatic camera is combined with an appropriate wavelength selection
system and acquires a variable number of spectral images of a scene. These images are then stacked
into a reflectance imaging cube to reconstruct reflectance spectra from each of the images’ pixels.
This paper presents an affordable multispectral imaging system composed of a monochromatic CCD camera and a set of only 12 interference filters for mapping pigments on works of art and for the tentative
identification of such pigments. This work demonstrates the versatility of this set-up, a versatility enabling it to be applied to different tasks, involving examination and documentation of objects of varying
size. Use of this multispectral camera for both panoramic and macro photography is discussed, together
with the possibilities facilitated from the coupling of the system to a stereomicroscope and a compound
microscope. This system is of particular interest for the cultural heritage sector because of its hardware
simplicity and acquisition speed, as well as its lightness and small dimensions.
Keywords: multispectral imaging; pigment identification; reflectance spectral imaging; reflectance
spectroscopy
Introduction
Reflectance imaging spectroscopy is used within art
examinations to visually enhance old documents (Kim
et al. 2011; Lettner et al. 2008; Padoan et al. 2008); to map
and identify pigments (Delaney et al. 2014; Melessanaki
et al. 2001; Ricciardi et al. 2009), as well as binders such
as animal glue and egg tempera (Dooley et al. 2013); and
to detect damage and areas of retouching (Pelagotti et al.
2008a). When pigments are mixed or glazed, reflectance
spectroscopy does not always provide conclusive identification unless the pigments used have very clear and
unique spectral features. In the opposite case, analytical examinations are recommended to produce detailed
diagnostic information. Nevertheless, reflectance imaging spectroscopy provides important information on the
materials present and can assist with the conservation
decision-making process.
Multispectral imaging equipment is commonly composed of a monochromatic camera: a CCD camera for
the UV-VIS-NIR range or a much more expensive InGaAs
camera for the SWIR (900–2500 nm) range. Some authors
have also explored the possibility of using a colour digital
camera (Blazek et al. 2013; Zhao et al. 2008). In general,
the reflectance spectral features in the UV-VIS-NIR range
* Cultural Heritage Science Open Source
(http://chsopensource.org), Piazza Cantarella 11,
Aci Sant’Antonio, 95025, Italy
antoninocose@gmail.com
are due to the electronic transitions responsible in part
for the colour of the pigments, while those in the SWIR
range are linked to the vibrational overtones. A wavelength selection system is added to the camera so that
it can capture images of an object in a series of spectral
bands. Once the images are registered and calibrated,
they are combined to form a reflectance image cube,
where the images are represented by the X- and Y-axes,
and where the Z-dimension denotes the wavelength of
each image. From the cube it is then possible to reconstruct the reflectance spectrum of each pixel. These systems are called multispectral if the number of spectral
images produced is less than, or in the order of, a dozen
(Pelagotti et al. 2008a; Pelagotti et al. 2008b; Toque et al.
2009) and hyperspectral if the number is higher. The multispectral group generally uses bandpass filters, which are
the simplest wavelength selection method. In contrast,
hyperspectral imagers can implement more advanced
components such as liquid-crystal tunable filters (LCTFs)
(Attas et al. 2003), acousto-optical tunable filters (AOTFs)
(Liang et al. 2010) or grating spectrometers (Delaney et al.
2010) to provide hundreds of spectral images. (In order
to avoid confusion, it must be noted that in conservation
science the term ‘multispectral imaging’ is also used for
the image documentation of art works with a collection
of broad spectral band images realized with different sensors and lighting sources such as ultraviolet fluorescence
photos, infrared reflectograms and X-ray radiographs
(Cosentino 2013).)
Art. 6, page 2 of 17
This paper discusses the application of a simple multispectral imaging system composed of a CCD monochromatic camera and a set of 12 bandpass filters. A larger
set of narrower filters would provide higher spectral
resolution (Kubik 2007) but would also be more costly
and require more intense illumination, constraints often
undesirable when analysing works of art. The bandpass filters were selected with different bandwidths not equally
spaced across the recorded spectrum, as is generally the
case (Delaney et al. 2014; Ricciardi et al. 2009). Other studies have already used a combination of narrow and large
bandpass filters (Liang et al. 2005), and, for this work, the
centre wavelength and the bandwidth of the set of filters
have been chosen in order to better represent the spectral
features of 54 historical pigments (Cosentino 2015).
This paper first addresses the documentation of a relatively large panel painting and then examines the coupling
of the system with a macro photography lens and with a
stereo or a compound microscope for the study of paint
cross-sections and single grains of pigment. These case
studies illustrate the technical solutions devised and show
for the first time that all of these examinations can be conducted using the same multispectral system coupled with
appropriate hardware and software tools. Multispectral
documentation of large works of art, such as frescoes, has
already been achieved (Liang 2012; Martinez et al. 2002),
and specific technical solutions have been provided using
custom-made panoramic heads, large X-Y scanning stages
and easels, and proprietary software. The coupling of the
proposed multispectral imaging system with a stereo
and a compound microscope is utilized specifically for
the examination of cultural heritage artefacts, including
cross-sections and slide-mounted paint samples.
This system provides a qualitative reconstruction of the
reflectance spectra of the pigments for the sole purpose
of segmenting the images of polychrome works of art. It
is suggested for conservators wanting to identify areas
of interest for further analytical investigation in order to
achieve conclusive results.
Instrumentation
The multispectral imaging system (see Figure 3) is composed of a PixelTeq SpectroCam VIS CCD camera and
12 interference filters commercialized by the same company. The SpectroCam VIS camera incorporates a highsensitivity 5 Megapixel CCD (Sony monochrome ICX285,
2/3”, sensing area 8.98 × 6.7 mm2) covering the range
360–1000 nm and a sequential filter-wheel. A set of
12 filters was chosen (centre wavelength / bandwidth,
nm): 425/50, 475/50, 532/16, 578/10, 620/10, 669/10,
680/10, 717/10, 740/10, 750/10, 780/20, 800/10. The
pertinent feature of the filter-wheel is that, because of its
Nikon lens adapter, it can accommodate normal photographic lenses, expanding, as will be discussed, the potential applications of the system for art examination. The
filter-wheel can accommodate only 8 filters and so the
12 filters were changed manually.
Calibration of the images acquired for panoramic
and macro photography was conducted using the AIC
(American Institute of Conservation) photo target for
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
in-scene reflectance. Its white, its black and its four grey
patches were used to calibrate the images by applying a
multi-point third degree polynomial calibration curve
using ImageJ (Schneider et al. 2012). These patches are
manufactured by X-Rite, and they are identical to those
used in the X-Rite ColorChecker and the ColorChecker
Passport. The patches are identified by the following designations (white to black): white; N8; N6.5; N5; N3.5;
and black. In the Munsell notation their corresponding
chromas are 9.5, 8, 6.6, 5, 3.5, 2, their sRGB values are
243, 200, 160, 122, 85, 52, and the reflectance across the
400–805 nm range covered by the interferential filters is
uniform. The multi-point third degree polynomial calibration using the sRGB values of the six swatches made it possible to correct for the spectral response of the CCD across
the spectrum and to normalize the spectral images based
on the white swatch.
The images were then registered using ImageJ. Dark current subtraction was not necessary because of the high
sensitivity of the camera and of the short exposure due to
the availability of high-intensity lighting. Flat field correction was not applied because the specific task of this study
was to evaluate this equipment for mapping historical
pigments and segmenting images of polychrome artworks
of very different sizes: it would have been impracticable
to set a flat field calibration procedure for the largest of
the artworks tested. Therefore, the decision was made simply to set the lights appropriately to best achieve uniform
illumination.
For the calibration of the images acquired with the stereomicroscope and compound microscope, the same AIC
photo target was used, but because of the high magnification, only the images of the N6.5 patch were acquired for
simple linear calibration.
HyperCube (US Army Geospatial Center) imaging spectroscopy software was used for the analysis of the multispectral images. The reflectance spectra reconstructed
from the 12 spectral images is here referred to with the
acronym MSI-12, and the spectra are represented in the figures with dots. The filters cover only the VIS-NIR range and
consequently standard halogen lamps without UV emission were used. All of the FORS (Fiber Optics Reflectance
Spectroscopy) spectra of pigments presented in this paper
belong to the downloadable online FORS spectra of historical pigments (Cosentino 2014a). Technical photography
was also performed on the panel painting case study to
complement the information provided by the multispectral camera. For this a Nikon D800 DSLR camera (36 MP,
CMOS sensor) modified for full-spectrum acquisition
(built-in IR filter removed) was employed. This camera
was used for visible (VIS), infrared (IR), infrared false colour (IRFC), infrared fluorescence (IRF), ultraviolet fluorescence (UVF) and ultraviolet reflected (UVR) photography
(Figure 1). These technical photographic methods and
the related imaging equipment and calibration procedures are described elsewhere, including the details of filters and lighting set-up (Cosentino 2014b; Cosentino et al.
2014). Infrared reflectography (IRR) (Cosentino 2014c) was
performed, within the same case study, with an InGaAs
camera (320×256 pixels) Merlin NIR by Indigo Systems.
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
Art. 6, page 3 of 17
Figure 1: Antonino Giuffrè, Visitation between Saint Joseph and Saint Zachary, Taormina (Sicily). Technical photography
documentation.
Results and Discussion
This work illustrates the application of a multispectral system for the examination of art and historical objects of
different sizes. First, the spectral documentation of a large
panel painting is discussed, involving adaptation of the
panoramic photographic method. Then, a series of smaller
case studies are examined using a macro lens, a stereomicroscope and, finally, a compound microscope.
1. Panoramic Photography of a Large Panel Painting
Multispectral imaging documentation was conducted on
a large panel painting (163 (w) cm, 170 (h) cm, the top
lunette 21 (h) cm): the Visitation between Saint Joseph
and Saint Zachary (1480–1490) by Antonino Giuffrè
(Figure 2). Giuffrè was a Sicilian painter active mostly
in Messina during the final decades of the 15th century
and was a follower of Antonello da Messina (Bongiovanni
2001: 56). He and other local artists were involved in replicating and diffusing the style of the Master with a number
of replicas. This panel painting is the only one confidently
attributed to Giuffrè and is housed in Taormina (Basilica
di San Nicolò), Sicily. There is an additional series of panel
paintings which have been attributed to him but the attribution was based only on stylistic considerations. This
painting was examined during its restoration treatment,
which took place in the Angelo Cristaudo Conservation
Studio in Acireale, Sicily.
Multispectral imaging documentation of large objects
requires a large X-Y scanner (Martinez et al. 2002) or the
acquisition of a high number of images and their mosaicking. A system for automatic acquisition and stitching of
multispectral images has been suggested, requiring the
employment of telescope optics (Liang 2012). The solution illustrated in this section instead considers a multispectral camera (SpectroCam VIS CCD) coupled with an
automatic panoramic head (GigaPan Epic Pro) to acquire
the images using the panoramic photographic method
(Cosentino 2013) (Figure 3). A 20 mm lens was used; this
provided an equivalent focal length of about 75 mm when
mounted on the SpectroCam. (The equivalent focal length
of a lens is calculated by multiplying its focal length by
the crop factor of the imaging sensor with which the lens
is being used (about 3.7 for the SpectroCam).) The camera
was set at a distance of 3.5 m and two 400 W halogen
lamps were used, allowing the painting to be mosaicked
using four sections, and achieving a resolution of 2 pixels/
mm sufficient for pigment mapping and segmentation on
large works of art (Dyer et al. 2013; Liang 2012).
The painting was also examined with 7 technical
photographs (resolution: 3 pixels/mm) to complement
Art. 6, page 4 of 17
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
Figure 2: Antonino Giuffrè, Visitation between Saint Joseph and Saint Zachary, Taormina (Sicily). Areas of interest and
points discussed.
Figure 3: Left, SpectroCam mounted on the GigaPan Epic Pro panoramic head. Centre, the spectral images acquired for
the four sections of the painting. Right, the stitched, registered and calibrated 12 spectral images of the Visitation.
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
the information provided by the multispectral imaging
system.
The technical photos provide valuable preliminary
diagnostics of the painting. Figure 4 shows that the face
of Saint Joseph (Area A in Figure 2) has been heavily
restored, as evident in the UVF image. UV fluorescence
photographs are used to identify different varnishes
and over-paintings and are a supplementary technique
for identifying pigments and binders (Dyer et al. 2013).
The UVF image also shows a strong pale-white UV fluorescence in correspondence to the original white parts of
the painting, suggesting tempera binder. There is also a
weak reddish fluorescence, attributable to vermilion laid
with tempera, corresponding with the red garments. UVR
photography is used to map retouching made with two
modern white pigments, zinc white and titanium white,
which strongly absorb UV light and appear dark, contrasting with lead white which reflects UV (Bacci et al. 2007).
The same figure shows that the white areas that appear
to be retouchings because of the darker tone in the UVF
image also appear black in the UVR, suggesting a restoration performed with titanium white. Zinc white is ruled
out because its characteristic yellow UV fluorescence is
not observed. The flat reflectance spectra of the original
white paint (Point 13) and the restoration paint (Point 12)
in Figure 5 rule out lithopone (a mixture of barium sulphate and zinc sulphide), which has characteristic absorption bands in the infrared (Cosentino 2014b). The red
Art. 6, page 5 of 17
pigment in Point 4 is original while the red paint in Point 3
is in-painting with modern cadmium red as revealed by
its infrared fluorescence in the IRF image (Figure 4). The
original and retouched red paints cannot be differentiated in any of the other technical photos, nor can they
be differentiated by their reflectance spectra, which are
very similar (Figure 5). Both of these red paints appear
brighter in the 620 nm image than in that at 578 nm, and
their reflectance spectra show a sharp inflection point at
600 nm, which suggests vermilion for the original paint
(Figure 5).
Area B is representative of the sky, which has original
blue paint, as well as numerous inpaints that become
evident in the spectral image at 800 nm (Figure 6). The
reconstructed reflectance spectrum of the original blue
pigment (Point 1) suggests azurite, and the areas retouched
(Point 2) are easily detected thanks to their sharp reflectance increase in the infrared region (Figure 6).
Area C is located on the landscape and has original green
paint (Point 5) and much retouching (Point 6), which
also become apparent in the spectral image at 800 nm
(Figure 7). The reconstructed reflectance spectrum of the
original paint (Point 5) features the broad reflectance maximum of malachite while the areas of retouching (Point 6)
show a maximum at 532 nm other than the sharp reflectance increase in the infrared region (Figure 7).
The Madonna’s mantle, Area D, has been heavily
restored to fill numerous lacunae. The reconstructed
Figure 4: Visitation between Saint Joseph and Saint Zachary. Area A in Figure 2. Technical photographs: visible (VIS),
ultraviolet fluorescence (UVF), ultraviolet reflected (UVR), infrared (IR), infrared false colour (IRFC) and infrared
fluorescence (IRF).
Art. 6, page 6 of 17
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
Figure 5: Visitation between Saint Joseph and Saint Zachary. Area A in Figure 2. Left, spectral images at 578 nm and 620 nm.
Right, MSI-12 spectra (dots) of Points 3, 4, 12 and 13 and FORS reference spectra of vermilion and cadmium red.
Figure 6: Visitation between Saint Joseph and Saint Zachary. Area B in Figure 2. Left, spectral images at 620 nm and 800 nm.
Right, MSI-12 spectra (dots) of Points 1 and 2 and FORS spectrum of azurite.
Figure 7: Visitation between Saint Joseph and Saint Zachary. Area C in Figure 2. Left, spectral images at 532 nm and 800 nm.
Right, MSI-12 spectra (dots) of Points 5 and 6 and FORS reference spectrum of malachite.
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
reflectance spectrum of the original paint (Point 8) suggests both malachite and retouchings (Point 9) are easily
detected because of their sharp reflectance increase in
the infrared region (Figure 8). The yellow vest of Saint
Joseph, within Area A, has been extensively retouched.
The reconstructed reflectance spectrum of the original
paint (Point 7) seems to indicate yellow ochre because of
the characteristic S-shape of ochre pigments (Figure 9).
Spectral images allow retouching to be better localized
and mapped than in the technical photographs. Figure 10
shows that the lacunae on the vest of Saint Zachary are
more easily distinguished in the 800 nm spectral image,
since with the high pass filter used for the infrared photography and with the IRR, both the original paint and the
Art. 6, page 7 of 17
retouching become transparent. The paints have much
greater contrast in the 800 nm spectral image as shown
by their reflectance spectra (Figure 9).
2. Macro Photography of a Postage Stamp
This multispectral imaging system allows for the documentation of small objects using standard macro photography lenses. Figure 11 shows the SpectroCam coupled
with the Nikon Nikkor Micro 105 mm f2.8 D. As previously discussed, because the CCD imaging sensor has
a high crop factor the resulting magnification is higher
than that produced with a full-frame digital camera. Calibration of the spectral images was performed using inscene small black and white reflectance references. The
Figure 8: Visitation between Saint Joseph and Saint Zachary. Area D in Figure 2. Left, spectral images at 620 nm and 800 nm.
Right, MSI-12 spectra (dots) of Points 8 and 9 and FORS reference spectrum of malachite.
Figure 9: Visitation between Saint Joseph and Saint Zachary. Area A in Figure 2. MSI-12 spectra (dots) of Points 7, 10 and
11 and FORS reference spectrum of yellow ochre.
Art. 6, page 8 of 17
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
Figure 10: Visitation between Saint Joseph and Saint Zachary. Area A in Figure 2. Technical photographs and spectral
image at 800 nm.
Figure 11: Left, SpectroCam equipped with a macro lens (Nikon Nikkor Micro 105 mm f2.8 D). Right, spectral images
at 578 nm and 620 nm of the postage stamp in the insert.
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
current filter-wheel can accommodate only 8 filters and
for the panoramic method discussed above the 12 filters
were changed manually. For this and the following photographic methods only the first 8 filters were used. Indeed,
manually changing the filters causes shaking of the camera that has little impact on the panoramic shooting, but
that is unacceptable for macro and micro photography. A
bigger filter-wheel or another technical solution is necessary to accommodate all 12 filters.
To test the usefulness of the spectral imaging system
combined with a macro lens, a postage stamp was examined. This stamp belongs to a private collection and was
issued by the Kingdom of Italy a few years before WWII.
Art. 6, page 9 of 17
Figure 11 shows the spectral images of the section (about
1 cm wide) of the stamp examined. The spectral images at
578 nm and 620 nm indicate that the red ink has a sharp
inflection point, and the reconstructed reflectance spectrum (Point 1, Figure 12) suggests the presence of madder lake, a common component of inks for postage stamps
documented for this period (Chenciner 2011: 201).
3. Stereomicroscope Photography for Detailed Pigment
Documentation
The SpectroCam was coupled to a stereomicroscope to
test its application for cases requiring higher magnification than macro photography (Figure 13). The test
Figure 12: Postage stamp. Left, spectral images. Right, reconstructed reflectance spectrum (dots) of the ink (Point 1)
and FORS reference spectrum of madder lake.
Figure 13: Left, SpectroCam coupled with the trinocular head of a compound microscope and a digital camera applied
on one of the eyepieces. Right, SpectroCam mounted on one of the eyepieces of a stereomicroscope.
Art. 6, page 10 of 17
subject was a cross-section taken from the painting
Madonna and Child attributed to Anton Raphael Mengs
(1728–1779) and conserved at KODE, Art Museums of Bergen (Figure 14). The spectral images (Figure 15) allow for
the reconstruction of the reflectance spectrum of the red
ground, which shows part of the S-shape characteristic of
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
ochre (Figure 16). Figure 17 shows the spectral images
acquired with the stereomicroscope of a small section
(about 2 mm wide) of the postage stamp already examined with the macro lens. The reconstructed reflectance
spectrum (Figure 16) provides the same conclusion as the
macro photography.
Figure 14: Anton Raphael Mengs, Madonna and Child. Courtesy of KODE, Art Museums of Bergen.
Figure 15: Madonna and Child, cross-section, Sampling Point 13 in Figure 14. SpectroCam mounted on a stereomicroscope, RGB image and spectral images.
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
Art. 6, page 11 of 17
Figure 16: MSI-12 spectra (dots) of the cross-section’s red ground, Point 1 in Figure 14, and of the postage stamp ink.
FORS reference spectra of red ochre and madder lake.
Figure 17: SpectroCam mounted on a stereomicroscope. Detail of the postage stamp in Figure 11. RGB image and
spectral images.
Art. 6, page 12 of 17
4. Micro Photography of Pigment Particles
The SpectroCam was coupled to a trinocular polarizing
microscope equipped with Epi-illumination (illumination from one side) and transmitted illumination. The
camera was mounted on the trinocular head using a
c-mount adapter, while a digital camera (Nikon D3200)
was applied on one of the eyepieces using an adapter
for Nikon digital cameras in order to record RGB images
(Figure 13). This set-up can obtain multispectral images
of slide mounts useful for pigment identification. This
application is particularly valuable for the analysis of pigment mixtures since the reflectance spectra can be used
to separate the components of the mixtures. Slide mounts
(Cargille Meltmount) of 5 historical pigments were tested.
Figure 18 shows the RGB image acquired with the digital camera of an azurite particle and its 8 spectral images.
The reconstructed reflectance spectrum successfully features the azurite maximum at about 450 nm (Figure 19).
Figure 20 shows the spectral images of a particle of
smalt and Figure 19 reports its reconstructed reflectance
spectrum, which represents satisfactorily the smalt broad
absorption band between the blue and infrared regions.
Malachite, another mineral pigment with relatively large
particles (Figure 21), could be identified by its broad
maximum (Figure 22). Analogously, the system proved
successful with vermilion, a mineral pigment with much
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
smaller particles (Figure 23). Its reconstructed reflectance
spectrum features its characteristic inflection point at
600 nm (Figure 22). The system was also able to reconstruct the reflectance spectrum of chrome green, a modern industrial pigment, showing its sharp maximum in
the green region (Figure 22).
Conclusions
This paper has illustrated the application of a simple
multispectral imaging system for the documentation
and examination of works of art and historical objects
of a wide range of dimensions. This system can mount
normal photographic lenses; consequently all of the photographic methods typically used for art documentation
can potentially be implemented. The illustrated case studies show that the reflectance spectra of the original and
retouching pigments could be differentiated and that historical pigments could be tentatively identified. The spectral images were also useful to map the filled lacunae and
in one instance performed even better than the infrared
technical photography because of the higher contrast in
the selected infrared band.
The study then addressed the implementation of
macro photography for the examination of a monochromatic postage stamp and continued with the coupling of the multispectral camera to a stereomicroscope
Figure 18: RGB and spectral images (objective 40X) of azurite slide mount.
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
Art. 6, page 13 of 17
Figure 19: Reconstructed reflectance spectra (dots) of particles of azurite and smalt on slide mounts and FORS reference spectra of azurite and smalt.
Figure 20: RGB and spectral images (objective 40X) of smalt slide mount.
Art. 6, page 14 of 17
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
Figure 21: RGB and spectral images (objective 40X) of malachite slide mount.
Figure 22: Reconstructed reflectance spectra (dots) of malachite, vermilion and chrome green particles and corresponding FORS reference spectra.
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
Art. 6, page 15 of 17
Figure 23: RGB and spectral images (objective 60X) of vermilion slide mount.
in order to reconstruct the reflectance spectrum of a
painting cross-section from the Madonna and Child by
Anton Mengs. Finally, the application of the camera on
a compound microscope to obtain reflectance spectra
of single pigment particles was discussed. These findings indicate the efficacy of coupling the proposed
multispectral imaging system with a stereo and a compound microscope for the examination of cultural heritage artefacts. The microscopy element of this tool is
able, tentatively, to identify pigments in cross-section at
much lower cost than techniques like SEM EDX (scanning electron microscopy with energy dispersive X-ray
spectroscopy), FT-IR (Fourier transform infrared spectroscopy) and Raman mapping spectroscopies. While
the latter techniques produce more accurate results, it
is proposed that the multispectral imaging system may
be used to widen accessibility to equipment, enabling
initial investigation of pigments, for example, during
preliminary conservation investigations and to identify
areas for more detailed analysis.
This paper has demonstrated the versatility of this simple multispectral imaging equipment and its capacity to
reconstruct the reflectance spectra of pigments observed
using different photographic and microscopic configurations to allow the mapping of historical pigments and
their tentative identification. The results of this work
encourage further study to develop the microscopy applications of this method and enhance the quality of the
reconstructed spectra with a larger set of filters and more
extensive tests on real artworks.
Competing Interests
The author declares that they have no competing interests.
Glossary
CCD camera. CCD (Charge-Coupled Device) cameras were
the first imaging sensors used in digital photography and
are now replaced by CMOS imaging devices. CCD technology is used in consumer digital photographic cameras as
Art. 6, page 16 of 17
well as sensitive scientific cameras, and their sensitivity
range is between about 350 nm and 1100 nm.
InGaAs camera. These cameras are sensitive to the near
infrared in the 900–1700 nm range and they are the
most common imaging device used to perform infrared
reflectography on works of art. Their name comes from
the Indium, Gallium and Arsenic which are present in the
imaging sensor.
UV, VIS, NIR, SWIR. Specifically related to the instruments discussed in this paper, these acronyms indicate
the following regions of the electromagnetic spectrum:
UV (Ultraviolet, 300–400 nm), VIS (Visible, 400–780 nm),
NIR (Near Infrared, 780–1100), SWIR (Short Wave Infrared,
1100–1700 nm).
Acknowledgements
This work has been possible thanks to PixelTeq, which
kindly provided the SpectroCam VIS and the filter
set presented in the paper. Special thanks also to the
Soprintendenza per i Beni Culturali di Messina, the
director of the restoration project, Dr. Grazia Musolino,
and to Angelo Cristaudo, restorer in Acireale, Sicily, for
providing access and permission to publish the results
on the Visitation between Saint Joseph and Saint Zachary by Antonino Giuffrè. Thanks also to the KODE, Art
Museums of Bergen, for permission to use the cross-section from their Madonna and Child, attributed to Anton
Raphael Mengs.
References
Attas, M, Cloutis, E, Collins, C, Goltz, D, Majzels, C,
Mansfield, J R and Mantsch, H H 2003 Near-infrared
spectroscopic imaging in art conservation: investigation of drawing constituents. Journal of Cultural Heritage, 4: 127–136. DOI: http://dx.doi.org/10.1016/
S1296-2074(03)00024-4
Bacci, M, Picollo, M, Trumpy, G, Tsukada, M and
Kunzelman, D 2007 Non-invasive identification of
white pigments on 20th century oil paintings by using
fiber optic reflectance spectroscopy. Journal of the
American Institute for Conservation, 46: 27–37. DOI:
http://dx.doi.org/10.1179/019713607806112413
Blazek, J, Soukup, J, Zitova, B, Flusser, J, Tichy, T
and Hradilova, J 2013 Low-cost mobile system for
multispectral cultural heritage data acquisition. In:
Proceedings of the Digital Heritage International Congress, IEEE: 73–79. DOI: http://dx.doi.org/10.1109/
digitalheritage.2013.6743715
Bongiovanni, G 2001 Giuffrè, Antonino. In: Dizionario
Biografico degli Italiani.
Chenciner, R 2011 Madder Red: A History of Luxury and
Trade. Routledge, Reprint edition.
Cosentino, A 2013 A practical guide to panoramic multispectral imaging. e-conservation Magazine, 25: 64–73.
http://www.e-conservationline.com/content/view/
1100 [Accessed 1 August 2014].
Cosentino, A 2014a FORS spectral database of historical
pigments in different binders. e-conservation Journal,
2: 53–65. http://e-conservation.org/issue-2/36-FORSspectral-database [Accessed 5 March 2015].
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
Cosentino, A 2014b Identification of pigments by
multispectral imaging; a flowchart method. Heritage
Science, 2: 8. http://www.heritagesciencejournal.com/
content/pdf/2050-7445-2-8.pdf [Accessed 5 March
2015]. DOI: http://dx.doi.org/10.1186/2050-7445-2-8
Cosentino, A 2014c Panoramic infrared reflectography.
Technical recommendations. International Journal of
Conservation Science, 5, 1: 51–60. http://www.ijcs.
uaic.ro/public/IJCS-14-05-Cosentino.pdf [Accessed 5
March 2015].
Cosentino, A 2015 Multispectral imaging system using
12 interference filters for mapping pigments. Conservar Património, 21. In Press. DOI: 10.14568/cp2015005
Cosentino, A, Caggiani, M C, Ruggiero, G and
Salvemini, F 2014 Panoramic multispectral imaging: training and case studies. Belgian Association of
Conservators Bulletin, 2nd Trimester: 7–11. http://
www.brk-aproa.org/uploads/bulletins/BULLETIN 2-14
kleur.pdf [Accessed 5 March 2015].
Delaney, J K, Ricciardi, P, Deming Glinsman, L,
Facini, M, Thoury, M, Palmer, M and René de la Rie, E
2014 Use of imaging spectroscopy, fiber optic reflectance spectroscopy, and X-ray fluorescence to map and
identify pigments in illuminated manuscripts. Studies
in Conservation, 59, 2: 91–101. DOI: http://dx.doi.org/
10.1179/2047058412Y.0000000078
Delaney, J K, Zeibel, J G, Thoury, M, Littleton, R,
Palmer, M, Morales, K M, René de la Rie, E and
Hoenigswald, A 2010 Visible and Infrared Imaging
Spectroscopy of Picasso’s Harlequin Musician: Mapping and Identification of Artist Materials in Situ.
Applied Spectroscopy, 64, 6: 584–594. DOI: http://
dx.doi.org/10.1366/000370210791414443
Dooley, K A, Lomax, S, Zeibel, J G, Miliani, C, Ricciardi, P,
Hoenigswald, A, Loew, M and Delaney, J K 2013
Mapping of egg yolk and animal skin glue paint binders in Early Renaissance paintings using near infrared
reflectance imaging spectroscopy. Analyst, 138: 4838–
4848. DOI: http://dx.doi.org/10.1039/c3an00926b
Dyer, J, Verri, G and Cupitt, J 2013 Multispectral imaging
in reflectance and photo-induced luminescence modes:
a user manual. The British Museum. http://www.
britishmuseum.org/pdf/charisma-multispectralimaging-manual-2013.pdf [Accessed 17 June 2015].
Kim, S J, Deng, F and Brown, M S 2011 Visual enhancement of old documents with hyperspectral imaging.
Pattern Recognition, 44, 7: 1461–1469. DOI: http://
dx.doi.org/10.1016/j.patcog.2010.12.019
Kubik, M 2007 Hyperspectral imaging: a new technique
for the non-invasive study of artworks. In: Creagh, D C
and Bradley, D (eds) Physical Techniques in the Study
of Art, Archaeology and Cultural Heritage, Vol. 2. Elsevier: 199–259. DOI: http://dx.doi.org/10.1016/S18711731(07)80007-8
Lettner, M, Diem, M, Sablatnig, R and Miklas, H 2008
Registration and enhancing of multispectral manuscript images. In: Proc. 16th European Signal Processing
Conference (EUSIPCO08), Lausanne, Switzerland.
Liang, H 2012 Advances in multispectral and hyperspectral imaging for archaeology and art conserva-
Cosentino: Panoramic, Macro and Micro Multispectral Imaging
tion. Appl Phys A, 106: 309–323. DOI: http://dx.doi.
org/10.1007/s00339-011-6689-1
Liang, H, Keita, K, Pannell, C and Ward, J 2010 A SWIR
Hyperspectral Imaging System for Art History and Art
Conservation. Fires & Congressos, Alicante, Spain.
Liang, H, Saunders, D and Cupitt, J 2005 A new
multispectral imaging system for examining paintings. Journal of Imaging Science and Technology, 49,
6: 551–562.
Martinez, K, Cupitt, J, Saunders, D and Pillay, R
2002 Ten years of art imaging research. Proceedings of the IEEE, 90, 1: 28–41. DOI: http://dx.doi.
org/10.1109/5.982403
Melessanaki, K, Papadakis, V, Balas, C and Anglos, D
2001 Laser induced breakdown spectroscopy and
hyper-spectral imaging analysis of pigments on an
illuminated manuscript. Spectrochim Acta Part B, 56:
2337–2346. DOI: http://dx.doi.org/10.1016/S05848547(01)00302-0
Padoan, R, Steemers, T, Klein, M, Aalderink, B and
De Bruin, G 2008 Quantitative hyperspectral imaging of historic documents. In: Proceedings of the 9th
International Conference on NDT of Art, Jerusalem,
Israel.
Pelagotti, A, Del Mastio, A and Cappellini, V 2008a
Multispectral and multi-modal imaging data processing for the identification of painting materials. In:
Art. 6, page 17 of 17
Castillejo et al. (eds.) Lasers in the Conservation of
Artworks, Taylor & Francis Group, London: 454–458.
Pelagotti, A, Del Mastio, A, De Rosa, A and Piva, A
2008b Multispectral Imaging of Paintings. A way to
material identification. In: IEEE Signal Processing Magazine, 27: 27–36. DOI: http://dx.doi.org/10.1109/
MSP.2008.923095
Ricciardi, P, Delaney, J K, Glinsman, L, Thoury, M, Facini,
M and René de la Rie, E 2009 Use of visible and infrared reflectance and luminescence imaging spectroscopy
to study illuminated manuscripts: pigment identification and visualization of underdrawings. In: Pezzati, L
and Salimbeni, R (eds.) O3A: Optics for Arts, Architecture,
and Archaeology II, Proc. of SPIE, 7391.
Schneider, C A, Rasband, W S and Eliceiri, K W 2012
NIH Image to ImageJ: 25 years of image analysis.
Nature Methods, 9: 671–675. DOI: http://dx.doi.org/
10.1038/nmeth.2089
Toque, J A, Sakatoku, Y and Ide-Ektessabi, A 2009
Pigment identification by analytical imaging using
multispectral imaging. In: 16th IEEE International Conference on Image Processing (ICIP): 2861–2864. DOI:
http://dx.doi.org/10.1109/icip.2009.5414508
Zhao, Y, Berns, R S, Taplin, L A and Coddington, J 2008
An Investigation of Multispectral Imaging for the Mapping of Pigments in Paintings. In: Proc. SPIE 6810, Computer Image Analysis in the Study of Art, San Jose, CA.
How to cite this article: Cosentino, A 2015 Panoramic, Macro and Micro Multispectral Imaging: An Affordable System for
Mapping Pigments on Artworks. Journal of Conservation and Museum Studies, 13(1): 6, pp. 1–17, DOI: http://dx.doi.org/10.5334/
jcms.1021224
Published: 17 July 2015
Copyright: © 2015 The Author(s). This is an open-access article distributed under the terms of the Creative Commons
Attribution 3.0 Unported License (CC-BY 3.0), which permits unrestricted use, distribution, and reproduction in any medium,
provided the original author and source are credited. See http://creativecommons.org/licenses/by/3.0/.
Journal of Conservation and Museum Studies is a peer-reviewed open access journal
published by Ubiquity Press.
OPEN ACCESS