Stranica 27 [27]
ka CHARISM A BI 7
Grant Agreement n" 228330
board, and the reflected light observed by the target camera. At the same time, the spectral
distributions of the monochromatic light are measured by a spectrometer. The camera
Spectral sensitivity can then be calculated using the captured images and measured
spectra.*’ This method is accurate as the measurements are independent of each other.
However, it requires expensive optical equipment and a dark room. Moreover, capturing
dozens of images and spectral distributions makes the whole procedure time-consuming,
restricting its use to well-equipped laboratories.
Figure 1-15. Visible-reflected image of a detail from a wall painting fragment from the British Museum
(Winged youth from the Tomb of the Nasonii, 1883,0505.5) as shot with; (a) a Canon 40D and (b) a
Fuji S3 Pro.
To simplify the procedure, methods which include calibration targets, in the captured image
such as the Macbeth colour chart discussed in the previous section have been proposed.
Various software solutions are available for calculating the 3x3 matrix coefficients, evaluating
the colour error and colour calibrating visible-reflected images using calibration targets. One
of these is an existing and already widely used workspace in nip2, as discussed above."
This module will thus be integrated into the workflow for the correction of reflected images,
as discussed in Chapter 3. The optimisation of experimental procedures, as well as the data
acquisition requirements for post-processing will be discussed in Chapter 2.
Version No. 1.0 19 Date : 14/10/2013