Usability of Digital Cameras for Verifying Physically Based ...

(a) (b)
(c)
Figure 52: Histograms of L ∗ a ∗ b ∗ differences for using the camera’s color space
for test cases (a) 8bit, (b) jpg and (c) 16bit.
we made a density plot of all values of test case one, ordered in the same way as
on the color chart (see figure 53). We can see that L ∗ a ∗ b ∗ differences are generally
low for dark patches and greenish patches like the ones in the bottom right corner.
Purple, red, and light blue patches seem to be a problem for color measurement.
As we found a tendency of certain colors to be reproduced less accurate than
others, we wanted to investigate, whether we can confirm this assumption. We
therefore compared measured L ∗ , a ∗ , and b ∗ values to the ones we calculated by
using the Adobe RGB ICC profile. Figure 54 shows the according plots. As L ∗
being the lightness of a color we can say that for high L ∗ values there is a tendency
to underestimation. For a ∗ values, that correspond to the redness and greenness of
a color we can see no clear color shift, but there is a clear overestimation for b ∗ ,
corresponding to the yellowness and blueness of a color.
To conclude, we can say that the mean and maximum values of all test cases
are quite high and can therefore not be considered as accurate measurements.
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