Master Thesis - Fachbereich Informatik

5.3. EXPERIMENTAL RESULTS 115
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Mean image brightness
Figure 5.10: Mean image intensity of a moving empty conveyor belt over time. The deviation
between the brightest and the darkest region on the conveyor exceeds 40 gray levels and is
originated in non uniform translucency characteristics of the belt. Example images showing
this non uniformity can be found in Figure 3.4.
as well as all other measurements belonging to this particular tube. It turns out that
the average ground truth distance of this tube is 0.3mm which is still larger than the
RMSE of the whole sequence due to the outliers. However it is shown that this tube is
not measured wrongly in general. Furthermore one can see that all neighboring tubes that
lie in the same region on the conveyor are also measured inaccurately. It is assumed that
with a more uniform conveyor belt such deviations could be avoided.
The mean over all measurements is 50.04 at 30m/min compared to 49.96 in the ground
truth. This is still very accurate. The precision of the vision-based measurements is
0.15 compared to 0.09 of human measurements under ideal laboratory conditions. The
corresponding Gaussian distributions are plotted in Figure 5.9(b).
Finally, the RMSE increases with faster velocities, and the total error is larger compared
to black tubes. The lowest error was measured at 20m/min (approximately the current
production velocity) with 0.11. This error is still only slightly larger than the human
variance.
One can conclude that the results of the black tubes are very accurate both for slow and
fast conveyor velocities. The RMSE falls even below the standard deviation of human
measurements. The accuracy of transparent tubes decreases with faster velocities, but is
still in a range that allows for measurements with the given tolerance specifications. Best
results have been achieved at a velocity of 20m/min. As it turns out, all tubes meeting the
tolerances in the real world (based on manual ground truth data) have been also measured
reliably to be within the tolerances by the system, i.e. ΩFN =0. Thus,notubewould
have been blown out wrongly at any velocity.