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Usability of Digital Cameras for Verifying Physically Based ...

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Figure 20: The CIE 1931 chromaticity diagram showing the wavelengths <strong>of</strong> light<br />

and the xy coordinates [cie06b].<br />

L ∗ �<br />

Y<br />

= 116<br />

a ∗ = 500<br />

b ∗ = 200<br />

Yn<br />

� � X<br />

� 1<br />

3<br />

− 16<br />

Xn<br />

� � Y<br />

Yn<br />

� 1<br />

3<br />

�<br />

Y<br />

−<br />

Yn<br />

� 1<br />

3<br />

�<br />

Z<br />

−<br />

Zn<br />

� � 1<br />

3<br />

where Xn, Yn and Zn are the tristimulus values <strong>of</strong> the reference white. For small<br />

values <strong>of</strong> V , V ∈ {X, Y, Z}, the normal <strong>for</strong>mulae are replaced by the following<br />

Vn<br />

modified <strong>for</strong>mulae:<br />

34<br />

� 1<br />

3<br />

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