Wireless Software Synchronization of Multiple Distributed Cameras

Abstract

We present a method for precisely time-synchronizing the capture of image sequences from a collection of smartphone cameras connected over WiFi. Our method is entirely software-based, has only modest hardware requirements, and achieves an accuracy of less than 250 µs on unmodified commodity hardware. It does not use image content and synchronizes cameras prior to capture. The algorithm operates in two stages. In the first stage, we designate one device as the leader and synchronize each client device's clock to it by estimating network delay. Once clocks are synchronized, the second stage initiates continuous image streaming, estimates the relative phase of image timestamps between each client and the leader, and shifts the streams into alignment. We quantitatively validate our results on a multi-camera rig imaging a high-precision LED array and qualitatively demonstrate significant improvements to multi-view stereo depth estimation and stitching of dynamic scenes. We release as open source libsoftwaresync, an Android implementation of our system, to inspire new types of collective capture applications.

Twist-n-Sync: Software Clock Synchronization with Microseconds Accuracy Using MEMS-Gyroscopes

“…Ansari et al [7] developed an Android app with their variant of NTP for clock synchronization and frame phases aligning algorithm to get sub-millisecond accuracy in an image capturing on mobile phones. Sandha et al [18] compared the performance of different synchronization tools available in smartphones (audio peripheral, Bluetooth, WiFi).…”

“…To demonstrate the quality of gyro-based synchronization on smartphones, we use and modify open-source Android application libsoftwaresync released by Google Research [ 7 ], which allows users to synchronously capture photos on multiple smartphones.…”

“… We carry out a deep analysis of gyroscope data and configurations that affect the accuracy of the method in order to provide a reference for the optimal choice of parameters. We deploy our method into our open-source publicly available Android Twist-n-Sync App [ 6 ], https://github.com/MobileRoboticsSkoltech/twist-n-sync , based on the work of Ansari et al [ 7 ]. We create a methodology and setup for estimation of synchronization accuracy and precision of our method on smartphones by using built-in rolling-shutter cameras.…”

“…We deploy our method into our open-source publicly available Android Twist-n-Sync App [ 6 ], https://github.com/MobileRoboticsSkoltech/twist-n-sync , based on the work of Ansari et al [ 7 ].…”

“…We deploy our method into our open-source publicly available Android Twist-n-Sync App [6], https://github.com/MobileRoboticsSkoltech/twist-n-sync, based on the work of Ansari et al [7]. • We create a methodology and setup for estimation of synchronization accuracy and precision of our method on smartphones by using built-in rolling-shutter cameras.…”