Hyperspectral imaging (HSI) is a non-invasive technique that utilizes a fully integrated camera, lighting, and software system for the capture of large format, high resolution images and standardized data output for the study of cultural heritage objects.
Images are taken with a 39 megapixel MegaVision monochrome camera. Monochrome images result in a high signal-to-noise ratio accomplished with less light needed on the object. Additionally, the monochrome images are completely registered - aligning all features on an image so that they match perfectly - to enable sharp, crisp, processing. A large field of view can be captured at a resolution of 300 dots per inch (dpi) with the capacity to zoom in to 6000 dpi for almost microscopic images. The inclusion of a dual color filter wheel allows enhanced assessment of UV fluorescence from excitation of various compounds and increased visibility of background or low-visibility information.
Illumination is provided by Equipoise LED low light, low heat lighting panel system in 14 wavelengths: Ultraviolet (365 nanometers), Visible (400, 450, 465, 505, 535, 592, 625, 637 nanometers), and Infrared (700, 735, 780, 870, 940 nanometers). Raking illumination is provided in two spectral bands (470, 910 nanometers) to illuminate from either side of the object at a low oblique angle. To minimize the impact of light on fragile items, the length of exposure of each individual light is carefully controlled through a maximized image histogram. The cool-light LED panels reduce light exposure to approximately 3.5 lux, as compared to normal room lighting at 350 lux.
Integrated in the PhotoShoot software is a specially developed metadata table to capture object identification, scientific, and spatial information to ensure long-term access, management, and use of the object. Our metadata standards encompass multiple domains and go beyond the provisions of any single existing metadata standard. The Library of Congress is pioneering an approach called "scriptospatial imaging" which utilizes geospatial software to spatially link data derived from the images to specific points on the images themselves, facilitating advanced data integration and access.
Images are produced in 16-bit TIFF format with an additional DNG copy for raw archival set purposes. The composite of each imaging wavelength creates an image cube where the resulting images may be digitally combined with or subtracted from each other to form images for scientific or scholarly analysis. HSI allows characterization of substrate (paper, parchment photographic processes) and colorants (dyes, pigments) based upon their specific spectral response in each wavelength. These specific spectral responses from compounds discriminate between similar materials and compounds, identifying and possibly quantifying materials present in the image. HSI allows the establishment of baseline data where deterioration assessment techniques can be linked to micro-analysis. The accurate determination of parameters associated with inks, pigments, colorants and base materials over time from a baseline response without sampling is critical to the assessment and preservation of many international items of cultural heritage.
- Establishing baseline images and spectral response data for deterioration studies, treatment evaluations, and monitoring fading/deterioration during exhibit
- Non-invasive characterization and mapping of past treatments on documents
- • Non-invasive characterization and imaging of pigments, inks, and colorants revealing text or images that have faded or been covered up, using advanced processing of data from discreet wavebands
Example project: Integrated Digital Imaging Systems: Hyperspectral Imaging