Gesture-Based Interaction with Time-of-Flight Cameras

CHAPTER 2. TIME-OF-FLIGHT CAMERAS
back to the detector. This implies that time-of-flight systems fall into the category of
active range imaging techniques.
Like TOF cameras, laser scanners can be used to implement this approach. A
major disadvantage of laser scanners is, however, that they can only measure the
distance to a single point in the scene at a time. Thus, they sweep the laser beam
across the scene to obtain an entire range image, which reduces the temporal of res-
olution of the imager.
2.3.5 Summary
In contrast to the above mentioned procedures to measuring range, a number of
advantages of the TOF sensor technology can be highlighted. These advantages can
roughly be divided into three categories: the robustness of the measurement, the
reliability of the hardware, and the cost of production.
As mentioned above, the most competitive alternative to TOF cameras are stereo
systems. However, one has to note that stereo systems only work under very restric-
tive constraints on the scene, i.e. the surfaces of the measured objects have to provide
sufficient texture for a robust estimate of the point-to-point correspondences. Here,
TOF cameras are less dependent on the scene and their main limitations in this con-
text are objects with specular surfaces. At the same time TOF cameras are widely
independent of the ambient light conditions as they rely on their own active illumi-
nation.
Although TOF cameras cannot match the accuracy of laser scanners they offer
the advantage that they use solid state sensor technology, i.e. the cameras are not
composed of moving parts which makes them very reliable and reduces maintenance
costs. Furthermore, they can achieve a higher temporal resolution as the range mea-
surement is computed in hardware in each pixel for an entire image and instead of
scanning the scene.
Finally, TOF cameras can be mass-produced at a very low cost because they are
based on standard CMOS technology. Thus, the sensor itself lies in the same price
range as regular 2D image sensors. Although, additional costs arise due to the illumi-
nation and control units, TOF systems are still cheaper than stereo cameras, which
generally involve two high quality imagers. Here, they also have the advantage of
being smaller in size.
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