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b. Setting up eguipment Below are some very general guidelines to the setting up of eguipment for multispectral imaging. Reference is made to existing manuals on the photography of works of art, in which these topics have already been dealt with in some detail. i. Location A designated space, preferably a studio, which can be darkened when required, is advised. Where a designated space is not available or when capturing images in the field or museum gallery, care should be taken to follow the optimised acquisition protocols as closely as possible and to accurately record the conditions under which images are captured. ii. Positioning the object For a general discussion and recommendations on the safe handling and positioning of objects for imaging in art historical and conservation contexts, the reader is referred to the AIC Guide to Digital Photography and Conservation Documentation " and other such manuals on the photography of works of art as referenced therein. iii. Positioning the camera and illumination sources For guidelines on the illumination of both two- and three-dimensional objects refer to the AIC Guide to Digital Photography and Conservation Documentation”? and other such manuals on the photography of works of art and scientific subjects as referenced therein. In addition, the reader is referred to Lighting Methods for Photographing Museum Objects.?° iv. Positioning the calibration targets The following guidelines are offered for the positioning of the Macbeth chart or X-Rite ColorChecker and the Spectralon diffuse reflectance standards (as available): 1) These should be positioned as centrally as possible within the frame and in line with the plane of the object (in as much as is possible). The post-processing workspace includes a function, to allow for some flexibility in the choice and number of Spectralon diffuse reflectance standards (see Chapter 3). This function allows the selection of the area sampled and enables the visualisation of these areas, which gives the user greater control of what is being sampled by the program, but in order for this to be effective, the available Spectralons need to be placed in a line and equidistant from each other, as shown in Figure 2-20(b). 2) Homogeneous illumination of the ColorChecker and Spectralon diffuse reflectance standards with no shadows should be ensured. 3) If images cannot easily be placed directly in the frame, “twin images” can be acquired by taking two images under exactly the same conditions. In one of these images, the ColorChecker and Spectralon diffuse reflectance standards are held in front of the object, as shown in Figure 2-20(b), where the targets are affixed to a rigid support with Velcro. Its “twin image” is recorded without the targets (Figure 2-20(a)). This is a particularly useful approach for field work. 4) A scale can also be inserted in the image if required. Version No. 1.0 59 Date : 14/10/2013 kanal
