CHSOS offers instruction on Technical Photography, Panoramic Infrared Reflectography, Reflectance Spectroscopy, Multispectral Imaging, Advanced Photographic Documentation.
Technical Photography (TP) (6 hours)
Technical Photography (TP) for Art diagnostics represents a collection of broadband spectral images realized with a modified digital camera (covering the 360-1100 nm spectral range), and different lighting sources and filters.
The Technical Photography (TP) Training module illustrates photographic methods in 3 spectral bands: Ultraviolet, UV (360-400 nm), Visible, VIS (400-780 nm) and Infrared, IR (780-1100 nm). We will practice 5 Technical methods: IR (Infrared), UVF (UV Fluorescence), UVR (UV Reflected), IRFC (Infrared False Color) and IRF (IR Fluorescence). These methods are used to reveal information such as underdrawing, pentimenti and inpaints. They can enhance the reading of faded documents and provide tentative identification of pigments.
Panoramic Infrared Reflectography (PIRR) (2 hours)
Panoramic Infrared Reflectography (PIRR) is a valid alternative to the much more expensive scanners for Infrared Reflectography (IRR) which is the imaging of works of art with a scientific camera in the range 1000- 1700 nm. Pigments such as azurite, Prussian blue and malachite become transparent only in the far infrared at about 1500 nm. The PIRR method consists of taking a series of images of a scene with a precision rotating head and then using panoramic software to align and stitch the shots into a single, seamless panorama. It can be implemented with consumer panoramic imaging tools, which can be upgraded following technical developments; as opposed to infrared scanners, which are products that cannot be modified. Self-assembled, modular equipment can be modified for specific tasks and upgraded with comparatively little funding, following technical and scientific developments in the consumer market, e.g. upgrading to an InGaAs camera with higher pixel count. The stitching software is easy to use; the overall panoramic method does not require specialized personnel or intensive training and, for these reasons the method is appealing to medium‐small museums and private conservators who want to implement an affordable method to professionally document their collections.
The Panoramic Infrared Reflectography (PIRR) Training module provides technical insight on hardware and software tools for PIRR using budget equipment already available commercially for panoramic photography along with an InGaAs camera.
Reflectance Spectroscopy (RS) (2 hour)
In the analysis of polychrome artworks, among the techniques available in portable version, Reflectance Spectroscopy (RS) has been established as a powerful one for the identification of pigments. A RS spectrum shows for each wavelength, the ratio between the intensity of the reflected light and the incident light, measured with respect to a standard white reference. This ratio is called reflectance and is given in percentage (%). The RS spectra can provide information useful for pigments identification since the radiation that is not reflected is absorbed or transmitted depending on the chemical composition of the material tested. The peculiar advantage of this method with respect to the other spectroscopies most commonly used, such as XRF and Raman, is that the RS equipment can be assembled with relatively low cost components.
The Reflectance Spectroscopy (RS) Training module discusses the procedures for pigments’ identification using a spectral database and our affordable spectrometer.
Multispectral Imaging (MSI) (6 hours)
Multispectral Imaging (MSI) is used to identify and map pigments in polychrome artworks and to enhance the reading of faded documents. Conservators can use this technique to distinguish original sections from inpaints and to select the proper conservation procedures. MSI analysis is based on the same concepts of Reflectance Spectroscopy but MSI has the added advantage that the pigments can be identified and mapped remotely on large areas rather than just a spot. Images of an object in a series of spectral bands are acquired, and once the images are registered and calibrated, they are uploaded into a Reflectance Image Cube. This represents the pixels of each image in the X and Y axes, while the Z dimension denotes the wavelength of each spectral image. From the cube, it is then possible to reconstruct the reflectance spectrum for each pixel of the image. Such systems are generally composed of a monochromatic camera (a CCD or an InGaAs camera) equipped with an appropriate wavelength selection system. These MSI systems are called multispectral or hyperspectral imagers depending on the number of spectral images produced; generally in the order of a dozen for the former, and many more for hyperspectral systems.
The Multispectral Imaging (MSI) Training module presents an affordable and open source MSI system developed in 2015 by CHSOS thanks to the first crowd-funded Research Project in Conservation Science – Multispectral Imaging (MSI) for Art and Archaeology – (43 contributions from 16 Countries). We will discuss the complete workflow for spectral images calibration, registration, and pigments mapping with this low-cost system which is composed of a commercial digital camera (modified to cover the 360-1100 nm range), 18 bandpass filters and free software. The advantages related to the implementation of a digital camera, rather than a monochromatic scientific camera, are significant. The same camera can be used for other methods, such as Technical Photography (TP), making the overall imaging equipment lighter and more versatile. This MSI system uses in-scene black, white and gray reference targets so it can be tailored to the needs of each specific art or archaeology documentation, using different lenses and lamps.
Advanced Photographic Documentation (APD) (2 hour)
The Advanced Photographic Documentation (APD) Training module presents a set of low-cost methods using a digital camera and few tools to complement an art and architecture examination.
- 360º virtual tours. The Training module shows how to create virtual tours and upload them into a webpage. They are useful to illustrate conservation projects, see Save the Soul of Savoca.
- Reflectance Transformation Imaging (RTI) is a computational photographic technique used in a number of fields related to art examination and documentation. RTI provides a virtual and enhanced visualization of an object’s surface where the lighting direction can be changed interactively and enhancements can be performed to make surface’ details more visible. It relies on the Polynomial Texture Map method which is an image-based representation of the object’s surface achieved by capturing the object under lighting from different directions. It is used to visualize tiny incisions in paintings and historical prints as well as to document highly reflective objects such as coins. The Training module illustrates our lightweight equipment for standard and macro RTI and the procedures to acquire and edit images to create the RTI visualization file.
- Focus Stacking photography. To document small artistic and historical objects, we use an automated macro rail for focus stacking, Photographing small objects that are flat is pretty simple and straightforward. On the other hand small objects that extend in space, as a piece of jewelry, are challenging because macro (close-up) photography implies very shallow depth of field. Even at large f-number it is possible to focus only a plane of the subject and the rest is out of focus. To get all the subject on focus it is necessary to use the focus stacking method.
- 3D Photomodeling. Photomodeling is the creation of 3D models from 2D pictures taken with an ordinary camera. This method is a cost-effective alternative to laser scanning , for fast documentation and survey, and the final model can be easily exported and shared. The Training module discusses the workflow using Agisoft PhotoSscan to produce 3D models and upload them on a webpage. They can be used to promote a conservation projects, see Catacombs, Syracuse, XIII century abside, Nunziatella.