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150} 100; Relative power 50} e A 0 a 4. 4. a 400 450 500 550 600 650 700 Wavelength A (nm) Relatíve power 60 Fale — ps0 = DSS 400 450 500 550 600 650 700 Wavelength A (nm) Figure 1-10. 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) captured with (a) tungsten lamps (represented by the CIE standard illuminant A) and (b) flashes (represented by the CIE standard illuminants D50 or D55).°° The manner in which cameras process images (see Chapter 3, section a) will also have an effect on the reproducibility of luminance in reflected images. The sensors used in DSLR cameras are linear, i.e. the number they generate for each pixel is proportional to the amount of light at that point. However, because the sensitivity of the human eye to light is different to that of a camera (Figure 1-11(a)), a function, or “gamma” is often applied to the captured image when this is converted into a standard J PEG or TIFF file by the camera or Version No. 1.0 Date : 14/10/2013 14
