Multispectral imaging is a non-destructive technique for painting investigation, successfully growing in the last few years. It provides a spectral and colorimetric characterisation of the whole painted surface. This is especially suitable both to identify the materials composing the painting surface, and to document its conservation state

The multispectral imaging technique consists in irradiating the artwork surface with visible and near infrared radiation, and detecting the diffused radiation within narrow spectral intervals.

Up till now, CCD or Vidicon cameras have been used to detect the back-scattered radiation. However, these devices present several drawbacks. The imaged area is generally non uniformly illuminated, the camera lens and the device intrinsic characteristics often introduce geometrical distortions which cannot always be correct for using image processing procedures. Moreover, the spatial resolution is in this case related to the dimensions of the area acquired, i.e, the larger the imaged area, the lower the resolution. In case of a large panel, in order to have high spatial resolution, it is therefore necessary to mosaic several images of smaller areas.

The GBC INOA scanning device for multispectral imaging and colorimetric characterization of paintings, has been specifically designed to overcome most of the problems related to the use of acquisition devices based on spatially-extended sensors, such as matrices or arrays.

The device will be using a purpose-built fast spectrophotometer for contact-less single-point spectral characterization, moved by XYZ-mounted translation stages. The scanning area will be 1m2 and the spatial resolution 16dots/mm2. An auto-focus system, both keep the painting surface on focus during the scanning even in case of irregular surfaces, and allow the simultaneous acquisition of the painting shape.
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