Multispectral Imaging Technology - Revealing What Lies Beneath the Mona Lisa

Table of Contents

Introduction
Multispectral Imaging
There’s More to Look at Than We Can See
What Lies Beneath

Introduction

The world has been captivated by Mona Lisa’s smile for centuries. Her identity and beguiling expression has resulted in a lot of analysis and speculation. Recently, an analysis, performed by French Scientist Pascal Cotte over a 10 year period, revealed a fascinating discovery: a hidden painting underneath.

Using the ‘Layer Amplification Method’ (LAM), which was pioneered by Cotte himself, he projected powerful beams of light at the painting and measured the reflections at varying wavelengths. This method, which reflects elements of multispectral imaging, has allowed Cotte to differentiate details between the various layers of paint and reconstruct what he believes to be the real painting underneath, what he calls ‘the real Lisa’.

Multispectral Imaging Technology and the Mona Lisa

Cotte was one of the only two people permitted by the Louvre to use scanning technology on the portrait.

We can now analyze exactly what is happening inside the layers of the paint and we can peel like an onion all the layers of the painting. We can reconstruct all the chronology of the creation of the painting.

Pascal Cotte, Scientist

His discovery made significant waves in the news, with it being claimed as “one of the stories of the century.” However, no definitive answers are guaranteed from a new imaging technique. It all relies on the applications, and Cotte’s claims have been met with criticism. Arts editor Will Gompertz told the BBC that, “The data that the technology generates is open to interpretation, which needs to be analyzed and corroborated by the academic and curatorial community, and not just an individual. I think the Louvre’s decision not to make a comment is telling.” The ‘technology’ that Gompertz refers to is mainly that of ‘multispectral imaging’, and is employed in many other industries, albeit for much different reasons.

Multispectral Imaging:

There’s More to Look at Than We Can See

Imagine reading The Odyssey, but the only letters one can understand are l, r, and y. Although one might have some information, it would be so incomplete it would be practically useless. The comparison is similar, when one thinks about part of the electromagnetic spectrum that is in fact visible to humans.

Multispectral Imaging Technology and the Mona Lisa

That small sliver between Infrared (IR) and UV (Ultraviolet) is what is known as the ‘Visible Spectrum’, and can be measured at wavelengths between 380 and 780 nm. The human eye cannot detect the remaining slivers, usually known as ‘spectral bands’.

As technology progresses, other spectral bands are continuously being harnessed in several ways for imaging applications. Radio telescopes are able to help map energy and objects in space by detecting radio waves, which pass comparatively easily through the atmosphere. X-ray is another example, which is a frequency that can pass through soft tissues, but bounces off bone, making it suitable for skeletal imaging.

Multispectral imaging can be defined as a process in which spectral bands are combined to produce different images. For instance, true color composites are images that signify natural renditions of what the eye can see, for instance, tree leaves are green and the ocean is blue, and use the spectral colors from the visible spectrum. An example is given below:

Multispectral Imaging Technology

False color composites use colors within the visible spectrum and also those found outside of it like X-ray, ultraviolet and near-infrared. This combination is used in various imaging devices, but it is most commonly used in satellite imaging. An example of a false-color composite of Las Vegas is given below.

Multispectral Imaging Technology

Image courtesy NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team.

Three spectral bands are used in the picture shown above: green and red from the visible spectrum, and near-infrared from the non-visible spectrum. This combination is perfect for detecting vegetation, which appears as red, as it highly reflects near-infrared light. In addition, it can help Geologists assess the health of various landmasses with shots taken from satellites such as the Landsat 8, and also be used for reconnaissance by the military. Spectral reflectance signature refers to the extent to which certain substances reflect spectral bands. Different spectral bands are used based on which landscape or object is being observed.

Space observation is another field where multispectral imaging is used. It is largely used by the Hubble Space Telescope, which observes in near-infrared, visible light and near ultraviolet region. Most of the iconic space photographs we know today have been produced by the Hubble Telescope. These images are captured by the telescope as it is located beyond the Earth’s atmosphere, which absorbs ultraviolet light and infrared and obscures the perception of space. The difference between an image of the well-known Horsehead Nebula taken from a regular telescope from Earth, and that taken by the Hubble Telescope can be clearly seen in the image below:

The Horsehead Nebula IC434" and "Hubble Sees a Horsehead of a Different Color"

"The Horsehead Nebula IC434" by Rawastrodata, and "Hubble Sees a Horsehead of a Different Color" by ESA/Hubble.

What Lies Beneath

Despite being quite rare and new, Cotte’s use of multispectral imaging is not without precedent. A similar method was used by a team of Researchers in order to reveal the hidden information on a 500 year old map that was believed to guide Columbus on his legendary journey to the New World, and multispectral imaging data from satellites was also used by British Scientists for investigating coastal archaeological sites.

With the potential to permeate other industries, multispectral vision technology has been recently used in food production facilities where it has been used to inspect the microbiological quality of meat. In addition, it is being used as a method to assess the health of seeds, which could be of enormous value to the agricultural industry.

If this technology is used extensively, it could lead to more and more revelations in a wide range of industries. While people are not completely sold on Cotte’s discovery, its ability to reveal the artistic process of famous artists through various layers of their paintings, could be a revelation in its own right.

This information has been sourced, reviewed and adapted from materials provided by Teledyne DALSA.

For more information on this source, please visit Teledyne DALSA.

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