TECHNICAL FIELD OF THE INVENTION The present invention relates to a method and system of multispectral spectroscopy through tuneable multispectral reflectoscopy for examining and identifying art objects especially paintings.

BACKGROUND OF THE INVENTION For the examination of valuable objects it is already known the use of X-rays or UV-light radiation to scan a painting. However due to the short range of wavelengths the infiltration is not deep enough and the diffusively reflected radiation is not easy to collect for spectral analysis.

In addition the first preliminary sketch on the preparation surface which has been painted, past or later underdrawings, ancient damages non visible to the naked human eye, later interventions or overpaintings, hidden signatures, non visible legends, authenticity features cannot be detected since the overlying paint layers cannot become successively "transparent".

It is therefore a need for a novel powerful tool of investigation in art objects and particularly in paintings which enables both tuneable multispectral real time imaging, between 200 nm and 6000 nm, as well as simultaneous multispectral spectroscopic data acquisition from the same investigated region.

The term"infrared reflectoscopy"is used for tuneable infrared imaging in paintings, which constitutes a significant tool of investigation, especially when simultaneous spectroscopic data acquisition is performed in the same examined region, between 200 nm and 3500 nm.

At the same time, spectroscopic data are collected from every point of the studied area between 200 nm and 6000 nm with a Snm step through grey level measurements, after adequate infrared Reflectance (% R) curve calibration, taking into account the spectral detectability range of the infrared detector as well as the output power distribution of the radiation coming out through the micrometer slit assembly, of the monochromator in use.

Inorganic pigments can thus be identified and their physicochemical behaviour directly compared to the corresponding infrared images at selected wavelengths inside this area.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a method and system of tuneable multispectral real time imaging for art objects, between 200 nm and 6000 nm, and simultaneous multispectral spectroscopic data acquisition from the same investigated region as well, which overcomes the deficiencies of the prior art.

A further aspect of the present invention is to provide system of an infrared reflectoscopy particular useful for delivering excitation light to an art object and collecting responce light from said art object

In accordance with the above objects of the present invention, an infrared reflectoscopy system of tuneable multispectral real time imaging for art objects, between 200 nm and 6000 nm, is provided comprising at least an illumination source housing and power supply, a single element CaF2 condenser, wherein a variable focusing is performed, a spectral analysis device such as a monochromator and an input port with a micrometer driven slit assembly, and a lateral output port also with a micrometer driven slit assembly.

Further preferred embodiments of the present invention are defined in dependent claims 2 to 6.

Other objects and advantages of the present invention will become apparent to those skilled in the art in view of the following detailed description taken in conjuction with the accompanying drawings, wherein like reference numbers refer to similar parts throughout the drawings, and wherein: BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a block diagram of the infrared reflectoscopy system according to the present invention.

Fig. 2 shows a diagram of the power radiation curve per surface unit and wavelength in 0.5 m distance (mW/m2/nm) from the source according to the present invention.

Fig. 3 shows a diagram of the transmittance of a CaF2 condensing lens according to the present invention.

Fig. 4 shows a schematic configuration of the monochromator's assembly according to the present invention.

Fig. 5 shows a diagram of the total efficiency curve related to the three gratings according to the present invention.

Fig. 6 shows a diagram of the normalized power distribution of the monochromator per surface unit (mW/mm2) according to the present invention.

Fig. 7 shows a diagram of the normalized sensitivity curve of the infrared detector according to the present invention.

Fig. 8a shows an image in the visible area of the spectrum.

Fig. 8b shows the corresponding non-visible image under the image of Fig. 8a.

Fig. 9 shows a visible image of the under study area.

Figs. 9a to 9h show examples of the infrared images of the image of Fig. 9 at 800nm, 1200nm, 1400nm, 1500nm, 1660nm, 1700nm, 1800nm, respectively according to the present invention.

Fig. 10 shows a diagram of the normalized transmittance of the infrared detector's lens according to the present invention.

Fig. 11 shows a diagram of the TMRS spectrum: lower curve and the W/VIS/nIR spectrum: upper curve of the Cross area (1) of Fig. 9a according to the present invention.

Fig. 12 shows a diagram of the TMRS spectrum: lower curve and the UV/VIS/nIR spectrum: upper curve of the Halo area (2) of the Fig. 9a according to the present invention.

Fig. 13 shows a diagram of the TMRS spectrum: lower curve and the UVNIS/nIR spectrum: upper curve of the Background area (3) of the Fig. 9a according to the present invention.

DETAILED DESRIPTION OF THE INVENTION Referring to the Figure I of the drawings a block diagram of the whole system according to the present invention is shown. Said system comprises an illumination source housing and power supply (1), a single element CaF2 condenser (2), wherein a variable focusing is performed, a monochromator (3) comprising three gratings, an input port (4) with a Micrometer driven slit assembly, and a lateral output port (5) also with a Micrometer driven slit assembly.

The system further comprises a location for the painted artwork (6), a calibrated infrared. detector (7), a fluorite lens (8), a motorized focusing system (9) and a computer (10).

An excitation illumination source delivers output power in the wavelength range from 200nm to 6000nm. As illumination source is used a high intensity arc lamp such as 1 OOOW Xenon due to it's flat spectral irradiance inside the spectral band (Fig. 4). The lamp is located inside the illumination source housing (1) with a heat blowing assembly.

A power supplier is also provided.

A CaF2 lens system is also provided in order to condense most of the radiated power from the arc lamp into the input port (4) of the monochromator (3). The CaF2 condensing lens has been selected because it presents more than 90% transmittance between 0. 2um and Sum (Fig. 3). The lens system has the possibility to be motorized in order to move back and forth as the focal length changes according to the wavelength of the radiation. In this way the incident radiation power on the input port (4) of the monochromator (3) will be maximized for each wavelength.

The incident radiation is then guided inside the monochromator's assembly (3) using the appropriate mirrors Ml, M2, M3 and M4 (Fig. 4) on a three gratings turret. Each grating is used in order to spatially separate light of different wavelengths (Fig. 5). The desired monochromatic radiation is separated and guided to the lateral output port of the monochromator, as soon as the grating turret is rotated around its axis.

The slits of the input and output ports of the monochromator system are micrometrically adjustable. Thus the bandwidth of the radiated light can be increased or reduced. The minimum bandwidth containing a sufficient amount of radiation power is found to be 5nm.

The following gratings can be used according to their spectral band response (Fig. 5).

15'grating : from 200-550nm 2"''grating : from 550-1200nm 3rd grading: from 1200-3500nm The normalized output power distribution of the monochromator was measured and the obtained values between 800nm and 1900nm are presented in Fig. 6.

This is the real output power distribution of the overall tuneable illuminating system taking into account the arc lamp, the CaF2 condensing lens and the three gratings.

Further, the output radiation from the monochromator strikes on the painted surface of the under study artwork (6). The reflected radiation from the artwork is then collected by the IR detector (7), the sensitivity of which is presented in Fig. 7.

The effectiveness of the proposed methodology has been finally tested on a portable experimental icon of known stratigraphy (Fig. 8).

Infrared images were collected every I Onm from a delimited surface area (Fig. 8) inside which infrared spectroscopic data were simultaneously collected from 800nm to 1900nm on three distinct areas 1,2 and 3 in diffuse reflectance mode. Grey level measurements were then taken from the acquired infrared images (Fig. 9) using our tuneable infrared reflectoscopy assembly and the obtained results were processed after adequate calibration and corrections The experimental icon"Descent from the Cross". A Short description The original is from the Macedonian school of the 14h century and is outstandingfor the harmony of its colours, its plasticity and the perfection of its design. The icon includes two pictures, one over the other. The scene of the"Descent from the Cross"Fig 8a was painted over the icon of"Saint James"Fig 8b, which was half covered with an intermediate preparation layer. This intermediate layer constituted at the same time the preparation layer corresponding to the overlying picture of the"Descent from the Cross".

The overall procedure which was followed in order to obtain the desired spectral information from the monochromatic images which were already acquired using the tuneable infrared reflectoscopy system can be summarized as follows: The overall system according to the theory of signal processing and systems can be described by three subsystems with known transfer functions: The Tuneable Monochromatic Radiation Source (TMRS). The normalized, to the unit value, power distribution between 800nm and 1900nm of this subsystem is already presented in Fig. 6 and denoted by the signal M.

The artwork response which constitutes the reflectance coefficient for each wavelength, Rx, inside the specified bandwidth (800nm-1900nm) is denoted by R.

The infrared detector and lens assembly system (Fig. 7 and 10 respectively) are denoted by C and L respectively.

The output of the overall system constitutes an ensemble of infrared images acquired by the IR detector for each wavelength between 800nm and 1900nm. Grey level values were measured on the pre-delimited areas 1,2 and 3 (Fig. 9a) every 10nm through a specially created software. They are denoted by Ix.

The final goal is to calculate the signal Rx which is the reflectance coefficient of the measurement area of the artwork between 800nm and 1900nm, for each wavelength.

The signals M, R, C, L and I are the spectral responses of each subsystem displayed as follows.

INPUT: Tuneable Monochromatic Radiation Source Signal (M) ARTWORK: Transfer Function (R) Infrared detector and lens system; Transfer Functions (C, L) OUTPUT: Stored Images from the infrared detector system (1) Thus we can obtain the Rx signal using the following formula for each wavelength. <BR> <BR> <P>R, = x wherein k is the wavelength.<BR> <P>M, C, L,

This method is then applied on three selected surface areas of the experimental icon (Fig.

9a), and RA=f (wavelength) curves are presented in Figures 11, 12 and 13 corresponding to the three pre-delimited measurement areas 1, 2 and 3 respectively.

The infrared diffuse radiation has been collected by the infrared detector, which is constantly positioned in front of the painted artwork. Nevertheless its power distribution changes according to the wavelength and incident radiation angle.

The spectroscopic data can be recorded using a UV/VIS/nIR spectrophotometer in a diffuse reflectance mode.

The output infrared radiation power of the UVNIS/nIR spectrophotometer used and that of the tuneable infrared reflectoscopy assembly do not have equal values. Thus their penetration depth is not the same; consequently the infrared information coming from the paint layers being underneath unequally affected infrared spectra which is collected from the painted surface.

From all these obtained experimental results we can conclude that: -Rx=f (wavelength) curves seem to have nearly the same shape compared to that obtained through a UVNis/nIR spectrophotometer in diffuse reflectance mode, for the same pre- delimited surface areas; this is an encouraging recording.

- The system can be software and hardware automated as a whole.

- The infrared reflectoscopy can permit both, tuneable real time infrared imaging as well as infrared spectra acquisition, from every point of the painted surface under examination, inside the same spectral bandwidth. These spectra, R ?, =f (wavelength), will provide us with all the necessary information, thus substituting reference infrared spectra which are normally provided by an nIR diffuse reflectance spectrophotometer.

While preferred embodiments have been shown and described obviously minor modifications in design and construction can be effected in the invention without departing from the spirit and scope thereof, as defined in the appended claims.