Usability of Digital Cameras for Verifying Physically Based ...

Figure 19: (a) A schematic of the diffuse patch reflection test case; (b) Comparison
of the measured illuminance with the results of the photon map and Radiance
[SW04].
photon map calculations is shown in figure 19b. The vertical bars in the measured
data indicate the sensor tolerance. It can be seen that the curves fit quite well. The
average deviation for Radiance is 3%, while it is 2% for the photon map.
For the case study involving caustics, the aluminium light shelf was moun-
ted on the outside of the window in order to create a caustic directed toward the
ceiling. The accurate simulation of this effect was possible with both rendering
algorithms, though the calculations of Radiance were slightly more noisy than the
ones of the photon map algorithm. This is also reflected in the average deviations,
which are 7% for Radiance and only 2% for the photon map.
The third case study that is described in the paper is a generalization of the
diffuse patch reflection case and therefore a compound case study. The whole
interior of the box was covered with light gray molleton. The BRDF data had to
be corrected because the molleton parts were from different consignments. After
this adjustment, the average deviations were 1% for Radiance and 2% for photon
map.
Similar results were achieved for the fourth test case, a combination of the
light shelf caustic and the diffuse interreflection. Due to the correction of the
BRDF data, deviations averaged 1% and 2%, for Radiance and the photon map
respectively.
Both algorithms performed well and the relative deviations were consistently
within the estimated error margins. Nonetheless, this setup can only be used for
point samples but not for other purposes as for instance for verifying the exact
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