Multispectral Imaging uses single wavelength illumination to capture images of samples such as documents, paintings and drawings in order to reveal faded, obscured and altered detail.
Due to the use of wavelengths beyond the visible spectrum, in the IR and UV ranges, pigments, inks and paints can be separated due to their spectral signature.
To obtain highly detailed images illuminated with narrow wavelengths are generated by a bank of LEDs that are directed at the sample. The sample reflects a portion of the light which is imaged by the high resolution and high sensitivity monochrome formatted camera/sensor.
The reflected wavelength spectrum and intensity depends on the interaction with the substrate and the pigment. In some cases, fluorescence is induced and the reflected light has an increase in the longer wavelength content. Barrier filters are introduced to select the individual wavelengths to form different images.
The EV Systems (Research and Lite versions) use these principles within integrated configurations controlled by a computer operated by 'Photoshoot' software.
The software ensure correct calibration of all the images along with such factors as shading correction to create a set of image data for each sample. The multi-wavelength (spectral) data is saved for analysis locally or for more intense scrutiny at a later date. A special high performance lens is available for the system that provides imaging from IR to UV through the visible spectrum without refocusing.
As sample sizes, working environments and the number of wavelengths (often over 15 different wavelengths are used) vary, two different format systems are available. EV is the research version which is designed to be used in a darkroom on a large copy-stand, while EV-Lite is a portable unit with a semi-rigid cover that can be used away from the studio/lab. The EV model can be populated with more individual wavelength LEDs than the EV-Lite system. The EV-Lite is designed for up to A3 format documents, whereas the EV can image larger documents and can be directed horizontally for imaging hanging painting, documents, frescos and tapestries.
Some of the world's most famous documents, including the Gettysburg address (USA), Magna Carta (UK), Dead Sea Scrolls (Israel), the manuscripts at St Catherine's Monastry (Egypt) and The Diaries of David Livingstone (Scotland) have been imaged using these systems.