All depth-sensing technologies have their attendant advantages and disadvantages. There is no “one-size-fits-all” technology that is perfectly suited for every application. For this reason, you have to select the most appropriate technology for a particular application based on the operating requirements and conditions, or in some cases even apply multiple technologies that can complement each other, with one supplying capabilities that the other can’t.
For example, if you were designing a sensor package for an autonomous guided vehicle (AGV) for operation outdoors, you might combine a LiDAR sensor to provide long-range awareness of movement or obstacles with a stereo depth cameras to provide high-fidelity depth sensing capabilities at short range.
If you were designing a sensor package for a similar AGV designed to operations inside a warehouse with low light levels overall, you might substitute a Time-of-Flight (ToF) camera for the depth camera because of its low-light capabilities.
Like all depth sensing technologies, Time-of-Flight cameras have some disadvantages and limitations. However, ToF cameras also offer advantages that make them very useful in the right context.
Advantages of ToF Cameras
ToF cameras typically have no moving parts. This is true for all indirect ToF cameras, which use diffuse laser illumination, though some direct Time-of Flight Cameras do use MEMS (Micro Electro-Mechanical Systems) chips or other moving parts to direct the laser.
All ToF cameras are compact, lightweight, and relatively inexpensive. Depending on the power required for their laser emitters, they can be made small enough to embed in very small devices, including cell phones.
All ToF cameras can be operated in very low light conditions, or even complete darkness, since they provide their own laser illumination. The accuracy of ToF cameras is also superior to any other depth sensing technology except for Structured Light Cameras. They can provide accuracy to a range of 1mm to 1 cm, depending on the operating range of the camera.
Indirect ToF cameras in particular, provide very high resolution, high-fidelity depth information at up to 640×480 pixels (VGA resolution).
Because they scan the entire scene in a single shot, iToF cameras also operate very quickly, providing depth-sensing data at up to 60 frames per second. This makes iToF cameras very useful for a wide variety of high speed or real-time applications where continuous feedback is required.
ToF cameras are also more affordable to build and procure when compared to other depth-sensing technologies like Structured Light Cameras and LiDAR sensors.
Disadvantages of ToF Cameras
ToF cameras do have some disadvantages. In brightly-lit situations or outdoors, the light from the laser emitters can be washed out by ambient light.
ToF cameras can also be confused by highly reflective surfaces. Retroreflective materials like those used on safety vests are particularly problematic because they do not scatter or reflect light the way normal surfaces do.
Time-of-Flight cameras also have to be used in isolation, or if multiple cameras are used, the field of view covered by their emitters can’t be allowed to overlap, otherwise encroaching light from other ToF camera laser emitters can produce artifacts in the resulting depth map.
For this reason, other depth sensing technologies, like stereo depth cameras may be more effective for applications that require operating outdoors, or in situations where you might want to have multiple depth cameras operating in the same area. Even with stereo depth cameras you have to be careful when deploying multiple cameras since many of them rely on a projected laser light pattern for computing the depth of flat or featureless surfaces.
These disadvantages of ToF cameras can limit their usefulness in some applications. However, as ToF technology continues to evolve, it is becoming more robust and flexible. As an example, Sony Semiconductor Solutions recently released the IMX570 ToF Sensor, which features a “pixel drive” processing circuit to reduce the effects of unwanted ambient light. This improves the accuracy and effective operating range of the sensor in highly illuminated environments or outdoors under bright sunshine.
Explore ToF for Yourself
If you are considering applying ToF depth sensing technology for a project or application you are developing, we can help.
FRAMOS has created a ToF camera development kit for vision system engineers who are investigating Time-of-Flight technology, or who are working to develop ToF cameras for machine vision applications. The FSM-IMX570 development kit provides a robust framework that can help you develop a working prototype of an indirect Time-of-Flight (iToF) camera system based on Sony’s industry-leading iToF technology.
If you are interested in evaluating Time-of-Flight technology, the FSM-IMX570 DevKit can provide you with an easy way to experiment with the technology or to develop your own prototype camera system. Click here to see the development kit specifications.
