Usability of Digital Cameras for Verifying Physically Based ...

(a) (b)
Figure 48: (a) The measurement points at 45 ◦ ; (b) absolute difference in luminance
for the 20 measurement points, accordingly.
the luminance difference distribution might be more even:
• we rotated it by 45 ◦ ,
• we placed it at a height of 24.5cm and
• we put it inside a black box.
Figures 48, 49 and 50 show (a) a photo of the measurement setup and (b)
the relative error in luminance, respectively. During the measurement process
the light cabinet again was covered with cardboard. The standard deviations are
26.97, 27.93 and 7.39, respectively. All three tests did not bring the desired im-
provement, as even the setup including the black box has a higher standard devi-
ation than the plain light cabinet at 100% (standard deviation: 6.28).
In order to decide which dimmer setting to use, we took one photograph each
at dimmer settings 100%, 50%, 25% and 15%. The camera settings used are
shown in table 7. As the exposure time was twice as long when the light intensity
was halved, the images theoretically should be equal, or at least very similar. We
used two methods to judge the quality of the images:
• We opened the images in GretagMacbeth ProfileMaker “Camera” Tab, be-
cause in one of our methods (see section 7.2) we use this software. Profile-
Maker checks, if the image can be used for generating an ICC profile (e.g.
it analyzes the luminance difference distribution on the ColorChecker). We
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