Interference Avoidance for Two Time-of-Flight Cameras Using Autonomous Optical Synchronization

Abstract

Time-of-Flight (ToF) cameras acquire 3-D images where each pixel relates to the distance in the observed scene. These images are acquired by emitting modulated light and measuring the phase of its reflection from an object. Improvements in ToF camera technology make it a promising alternative to current 3-D imaging sensors despite possessing comparatively lower resolution. Overcoming lower resolution, of single ToF camera images, is achieved using a multi-camera setup. However, the simultaneous operation of multiple ToF cameras causes interference resulting in erroneous depth measurements. An option to mitigate interference is the arrangement of multiple cameras in a consecutive order sharing the same frequency in assigned time slots, such that each camera illuminates the scene exclusively, a procedure known as time division multiple access (TDMA). The assignment of acquisition times is usually performed by a master synchronizing device implementing a time synchronization protocol that requires an additional communication channel. This paper presents a different approach requiring no additional infrastructure to utilize TDMA by adding a synchronization software procedure to the camera's microprocessor which effectively enables a camera to sense the acquisition process of other cameras and rapidly synchronize itself autonomously to operate without interference. Experimental results with two ToF cameras provide substantive evidence of the efficacy of this approach. The operation of the standalone cameras achieved the desired synchronization without illumination interference. The proposed synchronization procedure takes advantages of the zero interference of TDMA and overcomes traditional hard-wired synchronization setups, offering an autonomous and potentially mobile operation of ToF camera deployment.

A Review of Body Measurement Using 3D Scanning

“…Even though fast frame rates that are suitable for dynamic scanning can be achieved [51], [151], the biggest problem of single ToF camera scanners is a low scanning resolution [51]. It is possible to increase the resolution by using multiple ToF cameras [167], but complex light interference issues then need to be addressed [130]. Therefore, ToF is still less applicable for (quasi-) static scanning and body measurement.…”

Optical Synchronization of Multiple Time-of-Flight Cameras Implementing TDMA

“…ambient light conditions. The discussion section of [16] addresses the justification for this requirement.…”

“…The authors' previously published work presents a solution for zero illumination interference of two ToF cameras using *This research was performed in cooperation with iris GmbH and is cofinanced by the European Regional Development Fund (ERDF) time division multiple access (TDMA) [16]. TDMA allows several ToF cameras to operate sharing the same frequency channel by dividing the available channel access times into sequential repeating time slots, and assigning the cameras exclusively to one slot, resulting in non-interfering illumination.…”

ToF Image Sensor with Pulse-Frequency-Modulation Pixel for In-Pixel Code Discrimination

“…Several systems have been developed to deal with such interference light (IFL). [1] [2] remove it by post-processing pixel's output and [3] detects other cameras and drives the cameras in the way known as time division multiple access (TDMA). It's also effective to guarantee the correctness of measurement results by discriminating signal light (SGL) from the others.…”